feat(users): add Syncthing-menu to contributors page (#1022)

Signed-off-by: Ross Smith II <ross@smithii.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: rasa

users/contrib.rst

@@ -48,6 +48,10 @@ macOS / iOS
   Synctrain is an open source, native app for iOS, iPadOS and macOS that combines Syncthing with a file-centered UI with focus on selective and on-demand file synchronization.
   It can be installed from the `App Store <https://apps.apple.com/app/synctrain/id6553985316>`_.
 
+- `Syncthing-menu <https://github.com/gtunes-dev/syncthing-menu>`_
+
+  A frugal, native macOS menu-bar app for Syncthing.
+
 Linux
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