Merge branch 'gp/describe-match-uses-glob-pattern' into maint-1.8.1

The "--match=<pattern>" argument "git describe" takes uses glob
pattern but it wasn't obvious from the documentation.

* gp/describe-match-uses-glob-pattern:
  describe: Document --match pattern format

Author: gitster

Documentation/git-describe.txt

@@ -81,8 +81,9 @@ OPTIONS
 	that points at object deadbee....).
 
 --match <pattern>::
-	Only consider tags matching the given pattern (can be used to avoid
-	leaking private tags made from the repository).
+	Only consider tags matching the given `glob(7)` pattern,
+	excluding the "refs/tags/" prefix.  This can be used to avoid
+	leaking private tags from the repository.
 
 --always::
 	Show uniquely abbreviated commit object as fallback.