Add explanation to the help text on the new feature to build query st…

…ring from msg.payload

packages/node_modules/@node-red/nodes/locales/en-US/io/21-httprequest.html

@@ -61,6 +61,7 @@ <h3>Details</h3>
     url to be constructed using values of the incoming message. For example, if the url is set to
     <code>example.com/{{{topic}}}</code>, it will have the value of <code>msg.topic</code> automatically inserted.
     Using {{{...}}} prevents mustache from escaping characters like / & etc.</p>
+    <p>The node can optionally automatically encode <code>msg.payload</code> as query string parameters for a GET request, in which case <code>msg.payload</code> has to be an object.</p>
     <p><b>Note</b>: If running behind a proxy, the standard <code>http_proxy=...</code> environment variable should be set and Node-RED restarted, or use Proxy Configuration. If Proxy Configuration was set, the configuration take precedence over environment variable.</p>
     <h4>Using multiple HTTP Request nodes</h4>
     <p>In order to use more than one of these nodes in the same flow, care must be taken with