Update README.md and remove references to Bazel

[brendanhay]

Removes the references to Bazel and adds instructions for using Amazonka as a source/git dependency.

There's still no analogue to Bazel's //:docs target to build the website documentation - and as standalone-haddock is dead at this point it looks like waiting for cabal haddock-project to become generally available is more sane than the usual patching/templating/modifying Haddock's output to support a standalone bundle suitable and custom index/landing page for the website.

See:

• https://coot.me/posts/cabal-haddock-project.html

[brendanhay]

Is this it? Are we go for 2.0 RC 2?

Yes - although if there's no clear objective for RC2 I'd also be happy to just go for a 2.0 release proper?

[endgame]

I'd like to get one more round of botocore updates and checks for new regions etc in before we go to Hackage.