Replace book homepage with README

[ayberk]

What type of PR is this?

Uncomment only one, leave it on its own line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:
Moved README to /docs and set the /docs folder as the docs_dir so now README.md serves as the home page for the mkdocs.

Tested on my fork.

NONE

[nckturner]

Did the assets need to be included in the PR?

[nckturner]

To answer my previous question, looks like not. Another question -- should we 1. remove netlify, or 2. update it? cc @andrewsykim. I'm not sure I understand what benefit it provides.

[ayberk]

Well, it's hosted on Netlify and our subproject DNS points to that deployment(https://cloud-provider-aws.sigs.k8s.io/). I think I should be able to modify it to work. Let me try.

[ayberk]

/hold

[nckturner]

Oh got it. Yeah we should try to update it.

[ayberk]

/unhold

@nckturner Should be working now. deploy/netlify correctly renders the docs. I think it deploys to the actual site when we merge to master.

[nckturner]

Thanks
/lgtm

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