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](https://github.com/gabomdq/SDL_GameControllerDB). 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.

Start with the simple joystick example added in #27 and run it on Linux with a joystick. Check whether the device is detected but button presses are missed, then compare behavior when calling Raylib.SetGamepadMappings with a mapping from SDL_GameControllerDB. The work is done when it is clear whether the issue is the joystick mapping or the raylib_jll build.

Written by the indexing model from the issue text.