Add reference to rust-sdl2_ttf

[andelf]

Hi,
I've written the sdl2_ttf binding for Rust.
the repo is:
https://github.com/andelf/rust-sdl2_ttf

would you please add a reference link to my repo?

Best regards,
ShuYu Wang

[AngryLawyer]

Sure - pop it in a pull request and I'll merge it in :)