Test out joysticks on Linux

We now have a simple example of using Joysticks with Raylib added in #27. It works fine on Windows. However, when I test it on Linux, it doesn't work.

The program can detect the joystick correctly, but failed to detect any button press. It is an issue of missing gamepad mapping and can be solved by calling Raylib.SetGamepadMappings manually with the mapping found on the db. So the problem would be either I'm using an rare joystick or we didn't build the raylib_jll correctly so the mapping is missing on Linux.

We would need someone to test out joysticks on Linux to make sure it's not a problem of the jll.