Add hardhat readme

HARDHAT_README.md

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+[![Gitter chat](https://badges.gitter.im/sc-forks/solidity-coverage.svg)][18]
+![npm (tag)](https://img.shields.io/npm/v/solidity-coverage/latest)
+[![CircleCI](https://circleci.com/gh/sc-forks/solidity-coverage.svg?style=svg)][20]
+[![codecov](https://codecov.io/gh/sc-forks/solidity-coverage/branch/beta/graph/badge.svg)][21]
+[![hardhat](https://hardhat.org/buidler-plugin-badge.svg?1)][26]
+
+# solidity-coverage
+
+Solidity code coverage plugin for [Hardhat](http://hardhat.org).
+
+## What
+
+![coverage example][22]
+
++ For more details about how it works and potential limitations, see [the accompanying article][16].
++ `solidity-coverage` is also [JoinColony/solcover][17]
+
+
+## Installation
+
+```bash
+$ npm install --save-dev solidity-coverage
+```
+
+And add the following to your `.config.js`:
+
+```js
+require("solidity-coverage");
+```
+
+Or, if you are using TypeScript, add this to your hardhat.config.ts:
+
+```ts
+import "solidity-coverage"
+```
+
+## Tasks
+
+This plugin implements a `coverage` task
+
+```bash
+npx hardhat coverage [options]
+```
+
+| Option <img width=200/> | Example <img width=750/>| Description <img width=1000/> |
+|--------------|------------------------------------|--------------------------------|
+| testfiles  | `--testfiles "test/registry/*.ts"` | Test file(s) to run. (Globs must be enclosed by quotes.)|
+| solcoverjs | `--solcoverjs ./../.solcover.js` | Relative path from working directory to config. Useful for monorepo packages that share settings. (Path must be "./" prefixed) |
+| network    | `--network development` | Run with a ganache client over http using network settings defined in the Hardhat config. (Hardhat is the default network) |
+
+
+## Configuration
+
+Options can be specified in a `.solcover.js` config file located in the root directory of your project.
+
+**Config Example:**
+```javascript
+module.exports = {
+  skipFiles: ['Routers/EtherRouter.sol']
+};
+```
+
+| Option <img width=200/>| Type <img width=200/> | Default <img width=1300/> | Description <img width=800/> |
+| ------ | ---- | ------- | ----------- |
+| silent | *Boolean* | false | Suppress logging output |
+| client | *Object* | undefined | *Ganache only*: Useful if you need a specific ganache version. An example value is: `require('ganache-cli')` |
+| providerOptions | *Object* | `{ }` | *Ganache only*: [ganache-core options][1]  |
+| skipFiles | *Array* | `['Migrations.sol']` | Array of contracts or folders (with paths expressed relative to the `contracts` directory) that should be skipped when doing instrumentation. |
+| istanbulFolder | *String* | `./coverage` |  Folder location for Istanbul coverage reports. |
+| istanbulReporter | *Array* | `['html', 'lcov', 'text', 'json']` | [Istanbul coverage reporters][2]  |
+| mocha | *Object* | `{ }` | [Mocha options][3] to merge into existing mocha config. `grep` and `invert` are useful for skipping certain tests under coverage using tags in the test descriptions.|
+| onServerReady[<sup>*</sup>][14] | *Function* |   | Hook run *after* server is launched, *before* the tests execute. Useful if you need to use the Oraclize bridge or have setup scripts which rely on the server's availability. [More...][23] |
+| onCompileComplete[<sup>*</sup>][14] | *Function* |  | Hook run *after* compilation completes, *before* tests are run. Useful if you have secondary compilation steps or need to modify built artifacts. [More...][23]|
+| onTestsComplete[<sup>*</sup>][14] | *Function* |  | Hook run *after* the tests complete, *before* Istanbul reports are generated. [More...][23]|
+| onIstanbulComplete[<sup>*</sup>][14] | *Function* |  | Hook run *after* the Istanbul reports are generated, *before* the ganache server is shut down. Useful if you need to clean resources up. [More...][23]|
+
+[<sup>*</sup> Advanced use][14]
+
+## Usage
+
++ Coverage runs tests a little more slowly.
++ Coverage uses the Hardhat network by default.
++ Coverage [distorts gas consumption][13]. Tests that check exact gas consumption should be [skipped][24].
++ :warning:  Contracts are compiled **without optimization**. Please report unexpected compilation faults to [issue 417][25]
+
+## Using with ganache
+
+Begining with `v0.7.12`, this plugin runs directly on the Hardhat network by default (for speed).
+
+If you want to use a ganache based http network, you can specify it by name using the `--network` cli option. The plugin will then launch its own coverage enabled ganache instance which can be configured in `.solcover.js` via the `providerOptions` key.
+
+## Documentation
+
+More documentation, including FAQ and information about solidity-coverage's API [is available here][28].
+
+
+[1]: https://github.com/trufflesuite/ganache-core#options
+[2]: https://istanbul.js.org/docs/advanced/alternative-reporters/
+[3]: https://mochajs.org/api/mocha
+[4]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/faq.md#running-out-of-gas
+[5]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/faq.md#running-out-of-memory
+[6]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/faq.md#running-out-of-time
+[7]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/faq.md#continuous-integration
+[8]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/faq.md#notes-on-branch-coverage
+[9]: https://sc-forks.github.io/metacoin/
+[10]: https://coveralls.io/github/OpenZeppelin/openzeppelin-solidity?branch=master
+[11]: https://github.com/sc-forks/solidity-coverage/tree/master/test/units
+[12]: https://github.com/sc-forks/solidity-coverage/issues
+[13]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/faq.md#notes-on-gas-distortion
+[14]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/advanced.md
+[15]: #config-options
+[16]: https://blog.colony.io/code-coverage-for-solidity-eecfa88668c2
+[17]: https://github.com/JoinColony/solcover
+[18]: https://gitter.im/sc-forks/solidity-coverage?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge
+[19]: https://badge.fury.io/js/solidity-coverage
+[20]: https://circleci.com/gh/sc-forks/solidity-coverage
+[21]: https://codecov.io/gh/sc-forks/solidity-coverage
+[22]: https://cdn-images-1.medium.com/max/800/1*uum8t-31bUaa6dTRVVhj6w.png
+[23]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/advanced.md#workflow-hooks
+[24]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/advanced.md#skipping-tests
+[25]: https://github.com/sc-forks/solidity-coverage/issues/417
+[26]: https://hardhat.org/
+[27]: https://www.trufflesuite.com/docs
+[28]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/api.md
+[29]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/upgrade.md#upgrading-from-06x-to-070
+[30]: https://github.com/sc-forks/solidity-coverage/tree/0.6.x-final#solidity-coverage
+[31]: https://github.com/sc-forks/solidity-coverage/releases/tag/v0.7.0
+[32]: https://github.com/sc-forks/buidler-e2e/tree/coverage
+[33]: https://github.com/sc-forks/moloch
+[34]: https://github.com/sc-forks/solidity-coverage/blob/master/docs/advanced.md#reducing-the-instrumentation-footprint
+