Add examples + readme

[trappar]

Without more information this project looks interesting but I'm not sure how to even get started. Is this something you're going to be expanding on in the future?

[vladar]

Definitely. It's really in pre-release state now. We still explore usage scenarious ourselves and will probably make significant changes to API before first usable release.

But if you want to experiment with it, check out tests as usage examples, say:

https://github.com/webonyx/graphql-php/blob/master/tests/StarWarsSchema.php
https://github.com/webonyx/graphql-php/blob/master/tests/StarWarsQueryTest.php

[vladar]

Added quick README for now. Feel free to open specific issues if something requires additional clarifications in Readme.