Update "Shader compilation" in README

[timoffex]

The example was a bit outdated:

• Used the "package" terminology which has been replaced by "module"
• The import didn't work for me
• Missing parameter from ShaderCompileStep.create()

Side note: I don't really understand the purpose of the output flag parameter. What else can it be other than "-o"?

Side note 2: I'm new to Zig, and for some reason the alignment stuff doesn't work for me. I have to use the compiled shaders with @ptrCast(@alignCast(&my_shader)); the @as([*]const u32, @ptrCast(&my_shader)) approach doesn't work. If I knew the right way to do this, I would have included it in the example snippet.

[Snektron]

Thanks