chore: Add initial contributing help

CONTRIBUTING.md

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+# Contributing
+
+Welcome to the Arcjet JavaScript SDK! We're excited to have you contribute.
+
+Please review the guidelines we have below to help us in accepting your
+contribution.
+
+## Adapters
+
+New adapters are added to the root of this monorepo in the format of
+`arcjet-NAME_OF_ADAPTER` and the package name is `@arcjet/NAME_OF_ADAPTER`.
+
+For example, `arcjet-sveltekit` is the directory for the `@arcjet/sveltekit`
+package.
+
+Each new adapter should come with an example application in this repository. See
+[Examples](#examples) for guidance on creating an example.
+
+New adapters must also be added to our Release Please configuration files so it
+can be included in the next release. The two files that must be updated are
+[.release-please-manifest.json](./.github/.release-please-manifest.json) and
+[release-please-config.json](./.github/release-please-config.json). We can help
+you make changes to these files if you need help.
+
+## Examples
+
+Examples should be scaffolded using the scaffolding tool recommended by the
+framework. Generally, we choose all defaults for the example applications in
+this repository, but that is not a strict rule.
+
+When adding an example, it needs to be added to the
+[dependabot.yml](./.github/dependabot.yml) file and the
+[reusable-examples.yml](./.github/workflows/reusable-examples.yml) workflow. If
+the example does not have a build process to run in CI, it can be excluded from
+the workflow file.