Merge branch 'sb/doc-submodule-sync-recursive' into maint

* sb/doc-submodule-sync-recursive:
  document submodule sync --recursive

Documentation/git-submodule.txt

@@ -237,6 +237,9 @@ sync::
 +
 "git submodule sync" synchronizes all submodules while
 "git submodule sync \-- A" synchronizes submodule "A" only.
++
+If `--recursive` is specified, this command will recurse into the
+registered submodules, and sync any nested submodules within.
 
 OPTIONS
 -------
@@ -364,7 +367,7 @@ the submodule itself.
 for linkgit:git-clone[1]'s `--reference` and `--shared` options carefully.
 
 --recursive::
-	This option is only valid for foreach, update and status commands.
+	This option is only valid for foreach, update, status and sync commands.
 	Traverse submodules recursively. The operation is performed not
 	only in the submodules of the current repo, but also
 	in any nested submodules inside those submodules (and so on).