Instructions to debug Quicklink

CONTRIBUTING.md

@@ -18,11 +18,65 @@ again.
 ## Code reviews
 
 All submissions, including submissions by project members, require review. We
-use GitHub pull requests for this purpose. Consult
-[GitHub Help](https://help.github.com/articles/about-pull-requests/) for more
+use GitHub pull requests for this purpose. Consult [GitHub
+Help](https://help.github.com/articles/about-pull-requests/) for more
 information on using pull requests.
 
 ## Community Guidelines
 
 This project follows [Google's Open Source Community
 Guidelines](https://opensource.google.com/conduct/).
+
+## Debugging Quicklink
+
+The [test
+folder](https://github.com/GoogleChromeLabs/quicklink/tree/master/test) contains
+several test cases. Make sure to create a new test when building a new feature.
+
+Here's an example of how to debug the library by using one of these tests:
+[test/test-basic-usage.html](https://github.com/GoogleChromeLabs/quicklink/blob/master/test/test-basic-usage.html).
+
+1. Comment the following block of code at `test/test-basic-usage.html`:
+
+```javascript
+<script src="../dist/quicklink.umd.js"></script>
+  <script>
+    quicklink.listen();
+  </script>
+```
+
+2. Add the following snippet in its place, to import the module from its
+   source file:
+
+```javascript
+<script type="module"> 
+    import { listen } from "../src/index.mjs"; 
+    listen(); 
+</script>
+```
+
+3. Open
+   [src/index.mjs](https://github.com/GoogleChromeLabs/quicklink/blob/master/src/index.mjs)
+   for edit and replace the following line: 
+
+```javascript
+import throttle from 'throttles';
+``` 
+
+By:
+
+```javascript
+import throttle from '../node_modules/throttles/dist/index.mjs'
+```
+
+4. Build the project: `npm run build`.
+
+5. Start a local server: `npm run start`. By default, this will start the local server at `https://localhost:8080`.
+
+6. Open the file where the modifications where made:
+   `http://localhost:8080/test/test-basic-usage.html`.
+
+7. Open Chrome DevTools and go the **Sources** tab.
+
+8. Under `localhost:8080/src` you can find the unminified versions of the `Quicklink` files.
+   Now you can use breakpoints and inspect variables to debug the library.