Adds top level descriptions for error type enums.
Adds top level descriptions for error type enums.

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