add Markdown ref

templates/repo/comment_form.tmpl

@@ -9,6 +9,12 @@
                         <ul class="menu menu-line add-nav">
                             <li class="js-tab-nav js-tab-nav-show" data-tab-target="#commit-add-comment-form"><a href="#">{{$.i18n.Tr "repo.release.write"}}</a></li>
                             <li class="js-tab-nav" data-tab-target="#commit-add-comment-preview"><a href="#" id="pull-commit-preview">{{$.i18n.Tr "repo.release.preview"}}</a></li>
+                            <span class="text-right" style="float: right;">
+                                <a href="https://guides.github.com/features/mastering-markdown/" target="_blank">
+                                    <span class="octicon octicon-markdown"></span>
+                                    Markdown supported
+                                </a>
+                            </span>
                         </ul>
                     </div>
                     <div class="panel-content content">