> Is there anything else I need to add to get it to pick it up and work on /monitoring?
Do you have restarted the server? (it works for me with Bamboo 5.1.1)
> I think you've updated the documentation the wrong way round
Documentation seems ok to me:
atlassian-bamboo/WEB-INF/lib for Bamboo 5.1.1
webapp/WEB-INF/lib for Bamboo 4 and older
(English is not my mother tongue, so you can suggest a better wording if you want.)