Merge branch 'rj/clarify-branch-doc-m'

Doc update.

* rj/clarify-branch-doc-m:
  branch: clarify <oldbranch> term

Author: gitster

Documentation/git-branch.txt

@@ -312,7 +312,8 @@ superproject's "origin/main", but tracks the submodule's "origin/main".
 	option is omitted, the current HEAD will be used instead.
 
 <oldbranch>::
-	The name of an existing branch to rename.
+	The name of an existing branch.  If this option is omitted,
+	the name of the current branch will be used instead.
 
 <newbranch>::
 	The new name for an existing branch. The same restrictions as for