chore: Add instructions to CONTRIBUTING.md for manually enabling Email/Password authentication (#184)

* Resolve #183: Add instructions to CONTRIBUTE.md addressing manually enabling Email/Password authentication

* Address wording changes for CONTRIBUTING.md

* Split line exceeding 100 characters in CONTRIBUTING.md

Author: MathBunny

CONTRIBUTING.md

@@ -153,6 +153,13 @@ required to ensure that exported user records contain the password hashes of the
 3. Click 'ADD ANOTHER ROLE' and choose 'Firebase Authentication Admin'.
 4. Click 'SAVE'.
 
+For some of the Firebase Auth integration tests, it is required to enable the Email/Password
+sign-in method:
+1. Go to the [Firebase console](https://console.firebase.google.com).
+2. Click on 'Authentication', and select the 'Sign-in method' tab. 
+3. Enable 'Email/Password'.
+4. Enable 'Email link (passwordless sign-in)'.
+
 Finally, to run the integration test suite:
 
 ```bash