Prisma-client-js: Nested reads

[iherger]

I just discovered nested reads in #70

From my point of view, nested reads (using select and/or include) is actually really nice and very powerful.

I don't think this sufficiently described in the documentation, so I would suggest to add a paragraph about nested reads, e.g. in https://github.com/prisma/prisma2/blob/master/docs/relations.md#relations-in-the-generated-Photon-API

[ManAnRuck]

it would be also good for Nested Writes 🙏🏼

[nikolasburk]

Thanks for opening this issue @iherger 🙌 I've added some more docs around nested reads and writes (cc @ManAnRuck).

Note that the Photon.js will see some major updates soon (more info in the spec), so I'm sparing the work of going too deep into the documentation right now. The next version of the Photon.js API will be documented very thoroughly.