update oak-over-http documentation

It would be nice to update the wiki page in [0] about Oak over-http with some working example.

E.g using httpie

http -f -v -a admin:admin http://localhost:8080/ < samplenode.json

where samplenode.json is

{ "test4" :

{ "jcr:primaryType" : "nt:unstructured", "name" : "a node name" }

}

Thanks teofili for the working example

[0] http://wiki.apache.org/jackrabbit/Oak-over-HTTP