Clarify use for storing devise google data in callbacks controller

README.md

@@ -196,7 +196,8 @@ class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
         flash[:notice] = I18n.t 'devise.omniauth_callbacks.success', kind: 'Google'
         sign_in_and_redirect @user, event: :authentication
       else
-        session['devise.google_data'] = request.env['omniauth.auth'].except('extra') # Removing extra as it can overflow some session stores
+        # Useful for debugging login failures. Uncomment for development.
+        # session['devise.google_data'] = request.env['omniauth.auth'].except('extra') # Removing extra as it can overflow some session stores
         redirect_to new_user_registration_url, alert: @user.errors.full_messages.join("\n")
       end
   end