Docs: Update documents

Update folder structure in readme to align with build split change.
Specify eRPC test framework in index.rst otherwise it might mislead
users that eRPC test framework is the default one.

Signed-off-by: David Hu <david.hu@arm.com>
Change-Id: I444a4ca97a8b865a9222c4b373c5a758c2822fb0
2 files changed