doc: update Google SignIn integration documentation

doc/mobile-google-auth.md

@@ -1,22 +1,22 @@
 # Setting up Google Authentication
 
 - Create a Firebase project here: https://firebase.google.com/. You'll need a
-signed Android build for that, that can be a debug auto-signed build too, just
-retrieve the signing hash.
+signed Android build for that, that can be a debug self-signed build too, just
+retrieve the signing hash. The key hash of an already signed ap can be obtained
+as follows (on macOS): ```keytool -list -printcert -jarfile the-app.apk```
 - Place the generated ```google-services.json``` file in ```android/app```
 for Android and the ```GoogleService-Info.plist``` into ```ios/app/src``` for
 iOS (you can stop at that step, no need for the driver and the code changes they
 suggest in the wizard).
 - You may want to exclude these files in YOUR GIT config (do not exclude them in
 the ```.gitignore``` of the application itself!).
-- Your WEB and iOS client IDs are auto generated during the Firebase project
- creation. Find them in the Google Developer console:
- https://console.developers.google.com/
-- Make sure your config reflects these IDs so then the Redux state of the
- feature ```features/base/config``` contains variables
- ```googleApiApplicationClientID``` and ```googleApiIOSClientID``` with the
- respective values.
-- Add your iOS client ID as an application URL schema into
-```ios/app/src/Info.plist``` (replacing placeholder).
-- Enable YouTube API access on the developer console (see above) for live
+- Your web client ID is auto generated during the Firebase project
+ creation. Find them in the Google Developer console
+ (https://console.developers.google.com/)
+- Make sure your config reflects this ID by setting
+```googleApiApplicationClientID``` in config.js.
+- Add your iOS client ID (the REVERSED_CLIENT_ID in the plist file) as an
+application URL schema into ```ios/app/src/Info.plist```
+(replacing placeholder).
+- Enable YouTube API access on the developer console (see above) to enable live
 streaming.