Add a README for `clippy_lints`
Add a README for `clippy_lints`

This avoids the error:

> error: failed to read `/tmp/tralala/clippy_lints/README.md`

when publishing.

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