README.md was previously not very clear for newcommers, so make it clear
that the documentation contains a quickstart guide, and also add an even
quicker guide in-place for the lazy.

We also remove the instructions for building the documentation locally
and move it to the readthedocs documenation.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Removing references to cca config since that can't be used externally
for now. And provide instructions for building the container image since
external users don't have access to the repo.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>