Add documentation

The following guides were added:
* Setting up a RHEL 6.x IdM server with a Fedora 18 client
* Setting up and configuring swiftkerbauth
* Architecture of Swiftkerbauth

Change-Id: I50665e584ff9513b5a20d1eda546c73c93f14638
Signed-off-by: Prashanth Pai <ppai@redhat.com>
Reviewed-on: http://review.gluster.org/6040
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>