updated google.md doc for solving #581 (#970)

Author: faizplus

docs/config-examples/google.md

@@ -3,10 +3,11 @@
 Full support out of the box.
 
 ```js
+const GOOGLE_OAUTH_APP_GUID = 'YOUR_GOOGLE_OAUTH_APP_GUID' // it looks something like 12345678912-k50abcdefghijkabcdefghijkabcdefv
 const config = {
   issuer: 'https://accounts.google.com',
-  clientId: 'GOOGLE_OAUTH_APP_GUID.apps.googleusercontent.com',
-  redirectUrl: 'com.googleusercontent.apps.GOOGLE_OAUTH_APP_GUID:/oauth2redirect/google',
+  clientId: `${GOOGLE_OAUTH_APP_GUID}.apps.googleusercontent.com`,
+  redirectUrl: `com.googleusercontent.apps.${GOOGLE_OAUTH_APP_GUID}:/oauth2redirect/google`,
   scopes: ['openid', 'profile']
 };
 
@@ -26,5 +27,16 @@ await revoke(config, {
 
 
 ### Note for Android
+To [capture the authorization redirect](https://github.com/openid/AppAuth-android#capturing-the-authorization-redirect), add the following property to the defaultConfig in `android/app/build.gradle`:
+```
+android {
+  defaultConfig {
+    manifestPlaceholders = [
+      appAuthRedirectScheme: 'com.googleusercontent.apps.YOUR_GOOGLE_OAUTH_APP_GUID'
+      // your url will look like com.googleusercontent.apps.12345678912-k50abcdefghijkabcdefghijkabcdefv
+    ]
+  }
+}
+```
 - You need to check custom URI scheme under APIs & Services -> Credentials -> OAuth 2.0 Client IDs -> Your Client Name -> Advanced Settings
 - It may take 5 minutes to a few hours for settings to take effect.