Add docs for development

README.md

@@ -8,3 +8,15 @@ regarding issues automatically classified by our ML automation.
 
 * Go to a WebCompat issue in GitHub
 * A popup shows up for issues with useful classifications
+
+## Development
+
+* Install depedencies
+  * `npm install`
+* Run webextension for development
+  * `npm run firefox`
+* Run linters and prettier
+  * `npm run lint-js`
+  * `npm run lint-webex`
+  * `npm run prettier-check`
+  * `npm run prettier-write`