Add basic docs for 'init' command

[sake92]

Currently there is only one template. 😄
But I hope we will soon have more of them.

I made a PR for Play Framework seed playframework/play-scala-seed.g8#164

[lefou]

Looks good to me. Before merging it, I'd like to create / make sure that the referenced template under com-lihaoyi organization exists.

I need to learn a bit more about templates for this, as I still have open questions about your proposed template.

[ckipp01]

I'd like to create / make sure that the referenced template under com-lihaoyi organization exists.

When you do this we can also probably sunset https://github.com/scalameta/mill-scala-seed.g8 which we created so that when users do a new Scala project in Metals they got a mill option. We can change this to include the one from here then.

[lefou]

Thank you!