users: Add tooltip with group name in Roles list

This makes it clearer which group is being driven by the given
checkbox, whether 'wheel' or 'sudo' or 'docker' ... or others
in the future.

pkg/users/index.html

@@ -369,7 +369,7 @@ <h4 class="modal-title" translatable="yes">Add public key</h4>
   <script id="role-entry-tmpl" type="x-template/mustache">
     {{#roles}}
     <div class="checkbox accounts-privileged" data-container="body">
-      <label>
+      <label title="Unix group: {{name}}">
         <input type="checkbox" name="account-role-checkbox-{{id}}"
                data-gid="{{id}}" data-name="{{name}}"
                id="account-role-checkbox-{{id}}" {{#member}}checked{{/member}}/>