Issue #101 XML docs

 - Updated README
 - Added doc to the XSD
 - Added an annotated example XML
Well, initially the services were meant to be on top, as they are providing services to the caches declared below... not the only one we have right now it this 107 one, and that one actually doesn't provide a service to caches... So, not quite sure how we want to go about this really. I like the initial intent (all these services declared above, can be used by these Caches below)... I think we had a `<xs:any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>` at the end, which we eventually removed... We may want to consider adding this back, but also raises the question of what these would then be (something else than Services?) Or do we simple relax the rule, and make service, cache & cache-template freely inter mixable?
Whatever we decide, I'd do that as part of a different PR (and issue) though