fix a typo

* doc/tar.texi (Incremental Dumps): Add missing --file to the
'--list' example.

THANKS

@@ -140,6 +140,7 @@ Demizu Noritoshi	[email protected]
 Denis Excoffier         [email protected]
 Denis Fortin		[email protected]
 Dennis Pixton		[email protected]
+Derek Terveer           [email protected]
 Dick Streefland		[email protected]
 Dietmar Braun		[email protected]
 Dimitri Bougoulias	[email protected]

doc/tar.texi

@@ -6645,7 +6645,7 @@ especially, the binary output it produced were considered inconvenient
 and were changed in version 1.16.}:
 
 @smallexample
-@kbd{tar --list --incremental --verbose --verbose archive.tar}
+@kbd{tar --list --incremental --verbose --verbose --file archive.tar}
 @end smallexample
 
 This command will print, for each directory in the archive, the list