plug version example to the command call

doc/03-cli.md

@@ -401,7 +401,7 @@ This command is used to generate a zip/tar archive for a given package in a
 given version. It can also be used to archive your entire project without
 excluded/ignored files.
 
-    $ php composer.phar archive vendor/package --format=zip
+    $ php composer.phar archive vendor/package 2.0.21 --format=zip
 
 ### Options