Provide minimal quickstart .nengobones.yml file

[jgosmann]

It would be useful to have a minimal working .nengobones.yml file to get basic things running quickly and get a quick overview of the format (which I think the current documentation does not do a good job of). Maybe this file is already pretty minimal, but then it is quite a lot of boilerplate (and it definitely has some unnecessary environment variable defined).

[drasmuss]

Yes this is something we will add. For now though, the best place to start is probably https://github.com/nengo/nengo-dl/blob/master/.nengobones.yml, as the nengo-dl .nengobones.yml has the simplest configuration.