Add instructions for enabling autobinding

[jpwilliams]

The Getting Started guide doesn't mention that you need to enable autobinding to follow the final steps.

The gqlgen.yml file generated using the init command has autobinding disabled by default instead of enabled as the docs previously stated.

This tiny PR adjusts the guide to address this point.

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[coveralls]

Coverage decreased (-0.05%) to 74.446% when pulling c2ff419 on jpwilliams:patch-1 into 1324c3f on 99designs:master.

[StevenACoffman]

So... the difficulty here is that if you have previously generated no models, then there will be an error when you run gqlgen with autobind enabled since it won't be able to bind to those nonexistant models. That's why we disabled autobind for when people run init. Can you carefully verify that these updated directions work without any issue when you start completely fresh?

[jpwilliams]

@StevenACoffman Mm I suppose that could cause some problems if someone were to skip around the Getting Started guide rather than following every step. We could add a short note about when to enable autobinding (i.e. enable it if you've done the above step of creating a graph/model/todo.go file, otherwise don't)?

Have just tested again with a fresh repo following the adjusted Getting Started guide - works as expected.

[StevenACoffman]

Ok, I'm going to merge this as is, but if we start to get a lot of problems, then we can add a note. Thanks!