Explain how the GoReleaser automation works (#21)

Closes #5

Signed-off-by: Gerhard Lazu <gerhard@dagger.io>

Author: gerhard

README.md

@@ -5,6 +5,17 @@
 <!-- Remove this if you don't use github actions -->
 ![Build and populate cache](https://github.com/dagger/nix/workflows/Build%20and%20populate%20cache/badge.svg)
 
+This is updated by [GoReleaser
+Nixpkgs](https://goreleaser.com/customization/nix/) from within the
+[dagger/dagger](https://github.com/dagger/dagger/blob/v0.12.4/.goreleaser.yml#L31-L48)
+repository. GoReleaser runs in a `dagger` pipeline - [see the
+code](https://github.com/dagger/dagger/blob/v0.12.4/dev/cli.go#L184-L196). The
+entire release process - including this Nix flake - is captured in Dagger's
+[RELEASING
+documentation](https://github.com/dagger/dagger/blob/main/RELEASING.md). If
+you have more questions, [you can find us in our `#nix` Discord
+channel](https://discord.com/channels/707636530424053791/1122966469425233940) 👋
+
 ## Usage
 
 ### As flake