Update git submodules

* Update docs/submodules/releng from branch 'master'
  - xci: Update main script and readme

    This change
    - updates the main script to run the playbooks
    - creates the initial version of the readme file

    Change-Id: I4110433bce541a5d9645f34457f9e1b1ee93df19
    Signed-off-by: Fatih Degirmenci <fatih.degirmenci@ericsson.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index e40c112..9d7290a 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit e40c112a8127e2601e0e98e00598010120c8d41a
+Subproject commit 9d7290af5591ca634681845c50d079f095a6e03b