PCBC-173 Add couchbase.ini

This file describes the tunables, and may be installed on the target
system.

Change-Id: I1b67bbc03becc1f528e73dd772509dd914572624
Reviewed-on: http://review.couchbase.org/23634
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>