Note in te README about compiler version
Note in te README about compiler version

Closes #990

Emilgardis/rustfmt,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,SingingTree/rustfmt,studoot/rustfmt,rust-lang/rustfmt,aidancully/rust,SingingTree/rustfmt,graydon/rust,Emilgardis/rustfmt,aidancully/rust,studoot/rustfmt,aidancully/rust,graydon/rust,rust-lang/rustfmt,graydon/rust,aidancully/rust,aidancully/rust