gui: Add help link for sync protocol listen addresses

gui/default/syncthing/settings/settingsModalView.html

@@ -10,7 +10,8 @@
           </div>
 
           <div class="form-group">
-            <label translate for="ListenAddressesStr">Sync Protocol Listen Addresses</label>
+            <label translate for="ListenAddressesStr">Sync Protocol Listen Addresses</label>&emsp;<a href="https://docs.syncthing.net/users/config.html#listen-addresses" target="_blank"><span class="fa fa-fw fa-book"></span>&nbsp;<span translate>Help</span></a>
+
             <input id="ListenAddressesStr" class="form-control" type="text" ng-model="tmpOptions._listenAddressesStr">
           </div>
 
@@ -153,5 +154,5 @@
       <span class="fa fa-times"></span>&nbsp;<span translate>Close</span>
     </button>
   </div>
-  
+
 </modal>