Configure and document goreleaser

[bencromwell]

• is there a way to preview the changelog without having to nix and generate a new release?
• what other options are desirable?
• add release steps to the readme
• can it prep a release as a PR like release-please?

[bencromwell]

Snapshot lets you see the resultant changelog in dist/.

[bencromwell]

Should look at setting up a NUR for Nix and using it for this and git-spruce: https://goreleaser.com/customization/nix/?h=pull#cross-repository-pull-requests