doc: add URL.format() example

PR-URL: https://github.com/nodejs/node/pull/18888
Fixes: https://github.com/nodejs/node/issues/18887
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

doc/api/url.md

@@ -948,6 +948,20 @@ changes:
 The `url.format()` method returns a formatted URL string derived from
 `urlObject`.
 
+```js
+url.format({
+  protocol: 'https',
+  hostname: 'example.com',
+  pathname: '/some/path',
+  query: {
+    page: 1,
+    format: 'json'
+  }
+});
+
+// => 'https://example.com/some/path?page=1&format=json'
+```
+
 If `urlObject` is not an object or a string, `url.format()` will throw a
 [`TypeError`][].