docs: add a roadmap

[martinvonz]

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added tests to cover my changes

[PhilipMetzger]

This is a really nice Roadmap from all the discourse in the Discord from the last ~1.5 years.

[martinvonz]

I added a link to the roadmap from the top of the readme

[ilyagr]

Thank you, the roadmap looks nice to me!

This is very much non-blocking, but I would consider linking a Google Doc with the same roadmap, so that people can more easily start discussions about different parts of it. I was initially going to suggest only having a Google Doc, but on second thought, it's probably nice to occasionally to have more major updates this roadmap to go through a PR review and to have a commit description for them.

(Update: We could probably have a discussion about Google Doc on Discord if/when we feel like it, it might not really belong to this PR).

[martinvonz]

it's probably nice to occasionally to have more major updates this roadmap to go through a PR review and to have a commit description for them.

Yes, I think I would prefer that.

I'll probably merge in about a day. It sounds like there are no major objections to what's in here, so that's good. We can add more goals later as we think of them or as we reach a consensus on them.