Document how to define new lifecycle

Please update the documentation [1] to include how the plexus/components.xml can be included in the plugin, so that a new lifecycle or artifact handler can be defined, as described here [2]. It took me a week to find out (and also the mailing list was no big help BTW).

The solution is really simple, but if you don't know how to do it, it's not obvious. I've described it in my mail [3].

[1] http://maven.apache.org/guides/plugin/guide-ant-plugin-development.html
[2] http://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html
[3] http://www.mail-archive.com/users@maven.apache.org/msg37705.html