Add examples/readme

I would prefer it if #241 were resolved, but in the meantime ... I would suggest adding a readme explaining the differences between the examples as they currently are and normal application code.
The loader has nothing to do with the renderer used at runtime. The loader is really about being able to chose which mode (debug/whitespace/simple/advanced) to use. The loader used for the hosted examples is https://github.com/openlayers/ol3/blob/master/bin/loader_hosted_examples.js.