Improve next steps onboarding experience

[ahal]

We have decent documentation and tools to get set up with a working graph. There's taskgraph init and two tutorials that walk you through getting a hello world task running. We also have a decent amount of how-to guides and reference material.

But we're missing some stuff in-between. I had a conversation where someone was able to get a working hello world task, but was then lost about what to do next. I think we have a lot of room for improvement here. Some ideas:

1. A tutorial that walks through setting up an actually useful task (perhaps a lint, or a build)
2. Expand taskgraph init a bit to mimic real world usage a little more. Maybe a build, a test and a lint task.
3. ??? Ideas welcome