create a first usage example in readme

[e7dal]

something like this:

    <thing-prop name="name"></thing-prop> <!-- this will show the name of the thing -->
    <thing-prop name="manufacturer">
         <thing-prop name="name"></thing-prop> <!-- this will show the name of the manufacturer -->
    </thing-prop>
</thing>

Graphql equivalent:

    things(id: "123) { 
        name 
        manufacturer {
            name
        }
    }
}