Also add example for GitHub.

doc/integration/twitter_oauth.md

@@ -2,8 +2,11 @@ You can use Twitter to log into GitLab.
 
 Please configure this in gitlab.yml
 
-Below are screenshots how to setup your app on Twitter for this.
+Below are screenshots how to setup your app on Twitter for this:
 
 ![Application details](twitter_app_details.png)
 ![API Keys](twitter_app_api_keys.png)
 
+And GitHub:
+
+![GitHub app](github_app.png)