Add including headers description.

Add including headers description.

Change-Id: I304790db3f9346e7eb80a1e662dcbe4ba6d4a616
Signed-off-by: KIM JungYong <jyong2.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/13869
Reviewed-by: Uze Choi <uzchoi@samsung.com>
Tested-by: Uze Choi <uzchoi@samsung.com>
(cherry picked from commit 6eb9c9cfeacfd97fc92429fd524933713b698c8f)
Reviewed-on: https://gerrit.iotivity.org/gerrit/14807
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>