Added DevTools CONTRIBUTING guide

packages/react-devtools/CONTRIBUTING.md

@@ -0,0 +1,65 @@
+Intrested in contributing to React DevTools, but not sure where to start? This is the place!
+
+# Install project dependencies
+To get started, check out the React repo:
+```sh
+git clone git@github.com:facebook/react.git
+```
+Next install dependencies:
+```sh
+cd <react-repo>
+
+yarn install
+
+cd scripts/release
+yarn install
+```
+
+# Build React and React DOM
+Next, check out (or build) the local version of React that DevTools uses:
+
+### Option 1 (fastest): Checkout DevTools dependencies
+```sh
+cd <react-repo>
+scripts/release/download-experimental-build.js --commit=main
+```
+
+### Option 2 (if you've ade local changes to react): Build from source
+```sh
+cd <react-repo>
+yarn build-for-devtools
+```
+
+# Testing your changes
+
+### Option 1 (fastest): Using the test shell
+Most changes can be tested using the DevTools test app. To run this, you'll need two terminals:
+
+First, run DevTools in DEV mode:
+```sh
+cd <react-repo>
+cd packages/react-devtools-inline
+yarn start
+```
+Next, run the test shell:
+```sh
+cd <react-repo>
+cd packages/react-devtools-shell
+yarn start
+```
+Now any changes you make to DevTools will automatically reload in the test app at http://localhost:8080
+
+### Option 2: Using the extension
+Some changes requiring testing in the browser extension (e.g. like "named hooks"). To do this, run the following script:
+```sh
+cd <react-repo>
+cd packages/react-devtools-extensions
+yarn build:chrome && yarn test:chrome
+```
+This will launch a standalone version of Chrome with the locally built React DevTools pre-installed. If you are testing a specific URL, you can make your testing even faster by passing the `--url` argument to the test script:
+```sh
+yarn build:chrome && yarn test:chrome --url=<url-to-test>
+```
+
+# Finding the right first issue
+The React team maintains [this list of "good first issues"](https://github.com/facebook/react/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc+label%3A%22Component%3A+Developer+Tools%22+label%3A%22good+first+issue%22) for anyone interested in contributing to DevTools. If you see one that interests you, leave a comment!