Add Gaomon PD2200 to `list_supported_tablets.rst`

Tested on Windows and Mac OS with the official drivers, and Linux (GNOME Xwayland) without installing anything.

The controls are a bit janky on Linux: the wheel doesn't stay open without "Use mouse events for right- and middle-clicks", and the tablet buttons don't do what they're supposed to. I tried to configure them in the settings, but didn't have much success.