[alphastrata]

Updates the help-menu on the wgpu-runner to avoid others making the mistake I made here.

Before:

Usage: example-runner-wgpu.exe [OPTIONS]

Options:
  -s, --shader <SHADER>       [default: Sky]
      --force-spirv-passthru
  -h, --help                  Print help

After:

Usage: example-runner-wgpu.exe [OPTIONS]

Options:
  -s, --shader <SHADER>       which shader to run [default: sky] [possible values: simplest, sky, compute, mouse]
      --force-spirv-passthru
  -h, --help                  Print help

closes #253

[Firestar99]

fixing the output filename collision warning on windows without breaking android is not trivial, let's leave it as is for now
#255