Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Explain the need of having an ssh key

    In order for XCI to work, the user needs to have a ssh key. Explain
    that on the README and show the command to generate it.

    Change-Id: I517e15de15ba1b09977dbd62881bc2625c8b2833

diff --git a/docs/submodules/releng b/docs/submodules/releng
index e43f4a7..7136335 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit e43f4a702cbf8c26a4a32827a3823a18c187d10b
+Subproject commit 71363357702c788bd938564d589752a95990099d