Document how to build and use bindings

[Daniel J. H.]

Nowhere do we advertise that we merged node-osrm into this repo. - user's do not know.

This should be made clear in the readme.

We should port over the old quick start / docs explaining how to build the node bindings locally, how to run the tests, what's required (when not using mason), etc.

Note: this is not about documenting the node-osrm API.