build: agent-js peer dependencies (#161)

# Motivation

Developers may be using both [nns](/packages/nns) and [sns](/packages/sns) in their projects - as we do in [NNS-dapp](https://github.com/dfinity/nns-dapp/). That is s why, to help tree-shaking and avoid duplication of code, the libraries of this project need to reference [agent-js](https://github.com/dfinity/agent-js) as peer dependencies.

When we are building here both `nns` and `sns`, as both builds are standalone, `agent-js` libs get bundled within the outcome. Which is fine if the libraries were always use separately but unfortunately, as we noticed in NNS-dapp, when both are consumed app bundlers are not always able to tree-shake correctly the code afterwards. So developers might end-up with `agent-js` libs twice in their code.

# Breaking Changes

- set `agent-js` libraries as peer dependencies

# Tests

Libraries were locally bundled, then packed (`npm pack`) and integrated in NNS-dapp to build and run the dapp.

Author: peterpeterparker

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ### Breaking changes
 
+- `agent-js` dependencies set as `peerDependencies`
 - Sns canisters' classes renamed with prefix `Sns`
 
 ### Features

HACKING.md

@@ -52,3 +52,12 @@ The files of the [candid](./candid) folders are shared across packages. Their ar
 - `something.certified.idl.d.ts`: the typescript definition of the above factory file
 
 (1) auto-generated with [didc](https://github.com/dfinity/candid)
+
+# Update peer dependencies
+
+Saving peer dependencies in `package-lock.json` needs npm >= v7.
+
+```bash
+npm rm @dfinity/principal @dfinity/agent @dfinity/candid
+npm i @dfinity/[email protected] @dfinity/[email protected] @dfinity/[email protected] --save-peer
+```

README.md

@@ -11,6 +11,24 @@ The libraries are still in active development, and new features will incremental
 - cmc: querying the Cmc canister (_coming soon_)
 - [utils](/packages/utils): a collection of utilities and constants for NNS/SNS projects.
 
+## Installation
+
+Install [nns](/packages/nns) and/or [sns](/packages/sns) in your project from [npm](https://www.npmjs.com):
+
+```bash
+npm i @dfinity/nns
+npm i @dfinity/sns
+```
+
+You may be using both [nns](/packages/nns) and [sns](/packages/sns) in your project - as we do in [NNS-dapp](https://github.com/dfinity/nns-dapp/).
+That is s why, to help tree-shaking and avoid duplication of code, the libraries of this project are referencing [agent-js](https://github.com/dfinity/agent-js) as peer dependencies.
+
+Therefore, be sure that the needed `agent-js` dependencies are available in your project or install these as following:
+
+```bash
+npm i @dfinity/agent @dfinity/candid @dfinity/principal
+```
+
 ## Links
 
 Here are some useful links: