Remove links to empty markdowns on main page

For better readability to outside world.
As these markdowns have content, can be linked back.

Change-Id: I8b1646182f1a4b467ca66d68617e891b692c3e33
Reviewed-on: http://review.couchbase.org/34421
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>
Reviewed-by: Sriram Melkote <siri@couchbase.com>
Tested-by: Sriram Melkote <siri@couchbase.com>