Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Add dovetail tool CLI document

    According to the wiki page, add the CLI document.
    https://wiki.opnfv.org/display/dovetail/Dovetail+Command+Line

    JIRA: DOVETAIL-509

    Change-Id: I6a32446cd4c1bcad83465b1f2e12d5c1487e954e
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 931aa2b..fad3b8f 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 931aa2bae91dba172fb711960bc0ee5f9fc8a4c3
+Subproject commit fad3b8faebb29f79a6d6603ae21ccb5bf462574f