Update README.md

Author: SUPERCILEX

auth/README.md

@@ -199,26 +199,38 @@ startActivityForResult(
 
 #### Handling the sign-in response
 
-The authentication flow provides only two response codes:
-`Activity.RESULT_OK` if a user is signed in, and `Activity.RESULT_CANCELLED` if
-sign in failed. No further information on failure is provided as it is not
+The authentication flow only provides three response codes:
+`Activity.RESULT_OK` if a user is signed in, `Activity.RESULT_CANCELLED` if
+sign in failed, and `ResultCodes.RESULT_NO_NETWORK` if sign in failed due to a lack of network connectivity.
+No further information on failure is provided as it is not
 typically useful; the only recourse for most apps if sign in fails is to ask
 the user to sign in again later, or proceed with an anonymous account if
 supported.
 
 ```java
 protected void onActivityResult(int requestCode, int resultCode, Intent data) {
-   super.onActivityResult(requestCode, resultCode, data);
-   if (requestCode == RC_SIGN_IN) {
-     if (resultCode == RESULT_OK) {
-       // user is signed in!
-       startActivity(new Intent(this, WelcomeBackActivity.class));
-       finish();
-     } else {
-       // user is not signed in. Maybe just wait for the user to press
-       // "sign in" again, or show a message
-     }
-   }
+    super.onActivityResult(requestCode, resultCode, data);
+    if (resultCode == RESULT_OK) {
+        // user is signed in!
+        startActivity(new Intent(this, WelcomeBackActivity.class));
+        finish();
+        return;
+    }
+
+    // Sign in cancelled
+    if (resultCode == RESULT_CANCELED) {
+        showSnackbar(R.string.sign_in_cancelled);
+        return;
+    }
+
+    // No network
+    if (resultCode == ResultCodes.RESULT_NO_NETWORK) {
+        showSnackbar(R.string.no_internet_connection);
+        return;
+    }
+    
+    // User is not signed in. Maybe just wait for the user to press
+    // "sign in" again, or show a message.
  }
 ```