Adds warning about AWS usage while testing and puts in sample code to README.
Adds warning about AWS usage while testing and puts in sample code to README.

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