Add docs to sidebar

Author: tptee

website/gitlab.erb

@@ -90,6 +90,9 @@
           <li<%= sidebar_current("docs-gitlab-resource-project_variable") %>>
           <a href="/docs/providers/gitlab/r/project_variable.html">gitlab_project_variable</a>
           </li>
+          <li<%= sidebar_current("docs-gitlab-resource-service_github") %>>
+            <a href="/docs/providers/gitlab/r/service_github.html">gitlab_service_github</a>
+          </li>
           <li<%= sidebar_current("docs-gitlab-resource-service_jira") %>>
             <a href="/docs/providers/gitlab/r/service_jira.html">gitlab_service_jira</a>
           </li>