Document release cadence and roadmap

It would be very helpful to know when we can expect new releases (with our contributions!) and what the high-level roadmap is (e.g., Windows support).

The issue names no file, test, or entry point; start by locating the repository's release documentation and roadmap sources, then confirm the current release process with maintainers. Done means publishing a clear release cadence and high-level roadmap, including the status of Windows support.

Written by the indexing model from the issue text.