gui: Re-word introducer text (fixes #1819)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3831

gui/default/syncthing/device/editDeviceModalView.html

@@ -40,7 +40,7 @@
           <label>
             <input type="checkbox" ng-model="currentDevice.introducer"> <span translate>Introducer</span>
           </label>
-          <p translate class="help-block">Any devices configured on an introducer device will be added to this device as well.</p>
+          <p translate class="help-block">Add devices from the introducer to our device list, for mutually shared folders.</p>
         </div>
       </div>
       <div class="row">