Merge branch 'tz/doc-show-defaults-to-head' into maint

Doc update.

* tz/doc-show-defaults-to-head:
  doc: mention 'git show' defaults to HEAD

Documentation/git-show.txt

@@ -9,7 +9,7 @@ git-show - Show various types of objects
 SYNOPSIS
 --------
 [verse]
-'git show' [options] <object>...
+'git show' [options] [<object>...]
 DESCRIPTION
 -----------
@@ -35,7 +35,7 @@ This manual page describes only the most frequently used options.
 OPTIONS
 -------
 <object>...::
-	The names of objects to show.
+	The names of objects to show (defaults to 'HEAD').
 	For a more complete list of ways to spell object names, see
 	"SPECIFYING REVISIONS" section in linkgit:gitrevisions[7].