Adding anchors for references into kubref documentation

Adding anchors for references into kubref documentation

All three documentation items: installation instructions, user guide,
and configuration guide are all included in a single file, hence
adding all three anchors.

Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>
Change-Id: I4e43e286084ff598d007c9b6c0a03539d3ece136
Reviewed-on: https://gerrit.opnfv.org/gerrit/c/kuberef/+/72740
Tested-by: jenkins-ci <jenkins-opnfv-ci@opnfv.org>
Reviewed-by: Rihab Banday <rihab.banday@ericsson.com>
(cherry picked from commit 520e5b1bc37772d8ca9814054e49a047596fbe44)
Reviewed-on: https://gerrit.opnfv.org/gerrit/c/kuberef/+/72603