Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - Merge "docs: add Pod Descriptor Files information" into stable/euphrates
  - docs: add Pod Descriptor Files information

    Change-Id: I9ca83d2bc42cb15cd37aa3726c02c458fb8a0ea3
    Signed-off-by: Guillermo Herrero <guillermo.herrero@enea.com>
    (cherry picked from commit a9d51e138de235fe98ba686a8ef0ad22e2e975d5)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index 0f9d744..2eb688d 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit 0f9d744587a3ebf37b9f84a7ef73d9433961d317
+Subproject commit 2eb688d9bf92880107dfafd0591ee81ad8210416