Add release notes for 4.0.0 to doc tree, updating the index.html page
with reference to the new release notes.
Include a symlink in the base dir so packagers can find RELEASE-NOTES
Co-Authored-By: Ruby Loo <rloo@yahoo-inc.com>
Change-Id: I1a161b2c1d1e27268065b6b4be24c8f7a5315afb