Previously, the release process for wasi-sdk was undocumented and
manual. The `RELEASING.md` document in this commit describes the steps
necessary to publish a new version of `wasi-sdk` as a GitHub release and
provides helpful scripts to automate some of the steps.
With this in place, a future change could add a workflow trigger that
allows running the steps automatically in GitHub actions. Keeping the
steps as scripts in the repository, however, allows developers to re-run
steps themselves in the (likely) case that something goes awry.
Andrew Brown