Update Contributing.md and add information about ADR's (#383)

* Updating Contributing.md + add adr details

.github/CONTRIBUTING.md

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+# Contributions
+
+We welcome contributions in the form of issues and pull requests.  We view the contributions and process as the same for internal and external contributors.
+
+## Issues
+
+Log issues for both bugs and enhancement requests.  Logging issues are important for the open community.
+
+Issues in this repository should be for the toolkit packages.  Runner specific issues can be filed [in the runner repository](https://github.com/actions/runner).
+
+## Enhancements and Feature Requests
+
+We ask that before significant effort is put into code changes, that we have agreement on taking the change before time is invested in code changes. 
+
+1. Create a feature request. 
+2. When we agree to take the enhancement, create an ADR to agree on the details of the change.
+
+An ADR is an Architectural Decision Record.  This allows consensus on the direction forward and also serves as a record of the change and motivation. [Read more here](../docs/adrs/README.md).
+
+## Development Life Cycle
+
+This repository uses [Lerna](https://github.com/lerna/lerna#readme) to manage multiple packages. Read the documentation there to begin contributing.
+
+Note that before a PR will be accepted, you must ensure:
+- all tests are passing
+- `npm run format` reports no issues
+- `npm run lint` reports no issues
+
+### Useful Scripts
+
+- `npm run bootstrap` This runs `lerna bootstrap` which will install dependencies in this repository's packages and cross-link packages where necessary.
+- `npm run build` This compiles TypeScript code in each package (this is especially important if one package relies on changes in another when you're running tests). This is just an alias for `lerna run tsc`.
+- `npm run format` This checks that formatting has been applied with Prettier.
+- `npm test` This runs all Jest tests in all packages in this repository.
+  - If you need to run tests for only one package, you can pass normal Jest CLI options:
+    ```console
+    $ npm test -- packages/toolkit
+    ```
+- `npm run create-package [name]` This runs a script that automates a couple of parts of creating a new package.
+
+### Creating a Package
+
+1. In a new branch, create a new Lerna package:
+
+```console
+$ npm run create-package new-package
+```
+
+This will ask you some questions about the new package. Start with `0.0.0` as the first version (look generally at some of the other packages for how the package.json is structured).
+
+2. Add `tsc` script to the new package's package.json file:
+
+```json
+"scripts": {
+  "tsc": "tsc"
+}
+```
+
+3. Start developing 😄.