[WebUI] Add missing string

src/webui/www/public/preferences_content.html

@@ -81,7 +81,9 @@
     <li>QBT_TR(%Z: Torrent size (bytes))QBT_TR</li>
     <li>QBT_TR(%T: Current tracker)QBT_TR</li>
     <li>QBT_TR(%I: Info hash)QBT_TR</li>
-    </ul></i>
+    </ul>
+    QBT_TR(Tip: Encapsulate parameter with quotation marks to avoid text being cut off at whitespace (e.g., "%N"))QBT_TR
+    </i>
 </fieldset>
 </div>