Add Link to docs.growi.org (define .nav-item-help)

src/client/styles/scss/_layout.scss

@@ -17,7 +17,8 @@
     }
 
     .nav-item-admin,
-    .nav-item-create-page {
+    .nav-item-create-page,
+    .nav-item-help {
       span {
         margin-left: 0.5em;
         @media (max-width: $screen-xs-min) {

src/server/views/layout/layout.html

@@ -136,7 +136,7 @@
             <i class="icon-pencil"></i><span>{{ t('New') }}</span>
           </a>
         </li>
-        <li class="nav-item-admin">
+        <li class="nav-item-help">
           <a href="https://docs.growi.org/" target="_blank">
             <i class="icon-question"></i><span>{{ t('Help') }}</span><span class="text-muted small"><i class="icon-share-alt"></i></span>
           </a>