Fixes lib.rs link in codegen readme.
Fixes lib.rs link in codegen readme.

SecurityInsanity/rusoto,SecurityInsanity/rusoto,rusoto/rusoto,ford-prefect/rusoto,DualSpark/rust-aws,mthjones/rusoto,mattico/rusoto,DualSpark/rust-aws,rusoto/rusoto,indiv0/rusoto,cmsd2/rusoto,DualSpark/rusoto,mattico/rusoto,DualSpark/rusoto,rusoto/rusoto,DualSpark/rusoto,mthjones/rusoto,DualSpark/rust-aws,noggleboggle/rusoto,ford-prefect/rusoto,mattico/rusoto