Add pull request template.
Add pull request template.

rusoto/rusoto,SecurityInsanity/rusoto,DualSpark/rusoto,DualSpark/rust-aws,DualSpark/rust-aws,mattico/rusoto,DualSpark/rusoto,DualSpark/rusoto,DualSpark/rust-aws,mattico/rusoto,rusoto/rusoto,rusoto/rusoto,mattico/rusoto,SecurityInsanity/rusoto