Add help link

content/options.html

@@ -16,6 +16,10 @@
         <div>
           <div class="mdl-layout__header-row">
             <span class="mdl-layout-title">Markdown Viewer</span>
+            <div class="mdl-layout-spacer"></div>
+            <nav class="mdl-navigation">
+              <a href="https://github.com/simov/markdown-viewer#advanced-options" class="mdl-navigation__link">Help</a>
+            </nav>
           </div>
         </div>
       </header>