Add FAQ entry on whether to use winapi-rs or windows-rs

[slix]

This would be useful for people who need to choose a way to call Windows APIs.

I found little information online about making a choice:

• https://www.reddit.com/r/rust/comments/l23fr7/rust_for_windows_bindings_generating_the_entire/gk745dk/
• https://news.ycombinator.com/item?id=25866116
• Remaining code gen for windows-sys crate microsoft/windows-rs#1314

[Kreijstal]

@slix choose windows-rs, it has all functions you need, this was was hand-made and it feels like writing C code not Rust code, the windows one is more Rusty.