[Docs] Update nix dev env status

Summary:
Update status of Nix workflows.

Using this as a strategic guide on what to prioritize.

Test Plan:
https://github.com/CommE2E/comm/blob/jonringer/update-nix-status/docs/nix_dev_env.md
looks right given current tasks.

Reviewers: ashoat, varun, abosh

Reviewed By: ashoat, abosh

Subscribers: tomek, atul

Differential Revision: https://phab.comm.dev/D4926