chore(README): add a table of contents
chore(README): add a table of contents

Add a table of contents to the README, which includes links to information
relevant to Rusoto.
Move supported AWS services list to documentation website.

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