feat(contrib): mention Synctrain (#937)

Co-authored-by: tomasz1986 <[email protected]>

Author: pixelspark

users/contrib.rst

@@ -33,14 +33,19 @@ We currently don't have any actively updated Windows-specific GUI wrappers here.
 
 .. seealso:: :ref:`Cross-platform GUI Wrappers <contrib-all>`.
 
-macOS
-~~~~~
+macOS / iOS
+~~~~~~~~~~~
 
 - `syncthing-macos <https://github.com/syncthing/syncthing-macos>`_
 
   syncthing-macos is a native macOS Syncthing tray application bundle.
   It hosts and wraps Syncthing, making it behave more like a native macOS application and less like a command-line utility with a web browser interface.
 
+- `Synctrain <https://github.com/pixelspark/sushitrain>`_
+
+  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>`_.
+
 Linux
 ~~~~~