gui: Update link to send only documentation page

gui/default/syncthing/folder/editFolderModalView.html

@@ -84,7 +84,7 @@
           <div class="col-md-6">
             <div class="form-group">
               <label translate>Folder Type</label>
-              &nbsp;<a href="https://docs.syncthing.net/users/foldermaster.html" target="_blank"><span class="fa fa-book"></span>&nbsp;<span translate>Help</span></a>
+              &nbsp;<a href="https://docs.syncthing.net/users/foldersendonly.html" target="_blank"><span class="fa fa-book"></span>&nbsp;<span translate>Help</span></a>
               <select class="form-control" ng-model="currentFolder.type">
                 <option value="readwrite" translate>Send &amp; Receive</option>
                 <option value="readonly" translate>Send Only</option>