update Docker info

templates/install.tmpl

@@ -8,6 +8,8 @@
 			<div class="ui attached segment">
         {{template "base/alert" .}}
 
+        <p>{{.i18n.Tr "install.docker_helper" "https://github.com/gogits/gogs/tree/master/docker" | Safe}}</p>
+
 			  <form class="ui form" action="{{AppSubUrl}}/install" method="post">
 			  	<!-- Dtabase Settings -->
 			  	<h4 class="ui dividing header">{{.i18n.Tr "install.db_title"}}</h4>