Add a line about nightly builds to the readme
Add a line about nightly builds to the readme

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