Documentation/config.txt: Mention branch.<name>.rebase applies to "git pull"

Signed-off-by: Dustin Sallings <dustin@spy.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -362,7 +362,8 @@ branch.<name>.mergeoptions::
 
 branch.<name>.rebase::
 	When true, rebase the branch <name> on top of the fetched branch,
-	instead of merging the default branch from the default remote.
+	instead of merging the default branch from the default remote when
+	"git pull" is run.
 	*NOTE*: this is a possibly dangerous operation; do *not* use
 	it unless you understand the implications (see linkgit:git-rebase[1]
 	for details).