Fix broken homu link in CONTRIBUTING.md.
Fix broken homu link in CONTRIBUTING.md.

Fixes the docs aspect of https://github.com/rust-lang/rust/issues/43898.

GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust