doc: documentation of inode and dentry management

Change-Id: Ica510752d011596e8ecff5ea13c4b2bbf76ba186
BUG: 1145475
Signed-off-by: Raghavendra Bhat <raghavendra@redhat.com>
Reviewed-on: http://review.gluster.org/8815
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>