Update README. Recommend rustup.
Update README. Recommend rustup.

Also adds debugging info and contact info.

rust-lang/miri,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,rust-lang/miri,GBGamer/rust,aidancully/rust,rust-lang/miri,aidancully/rust,GBGamer/rust,graydon/rust,rust-lang/miri,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,tsion/miri,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust