add application check commands

doc/update/5.0-to-5.1.md

@@ -69,3 +69,22 @@ mysql> \q
 ## 7. Start application
 
     sudo service gitlab start
+
+## 8. Check installation
+
+
+```bash
+# In 5-10 seconds lets check gitlab-shell
+sudo -u git -H /home/git/gitlab-shell/bin/check
+
+# Example of success output
+# Check GitLab API access: OK
+# Check directories and files:
+#         /home/git/repositories: OK
+#         /home/git/.ssh/authorized_keys: OK
+
+
+# Now check gitlab instance
+sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
+
+```