Readme updates

Provided more info about links to forums and documentation etc. as well
as removed outdated info about linked repository to get started.

Change-Id: I3ec550d05e59de090b3d8d5c9896dea0687b3b7b
Reviewed-on: http://review.couchbase.org/27805
Reviewed-by: Saakshi Manocha <saakshi.manocha@globallogic.com>
Tested-by: Saakshi Manocha <saakshi.manocha@globallogic.com>