add completion to homebrew installation

Author: marceljk

.goreleaser.yaml

@@ -108,6 +108,9 @@ brews:
     # If set to auto, the release will not be uploaded to the homebrew tap repo
     # if the tag has a prerelease indicator (e.g. v0.0.1-alpha1)
     skip_upload: auto
+    install: |
+      bin.install "stackit"
+      generate_completions_from_executable(bin/"stackit", "completion")
 
 snapcrafts:
   # IDs of the builds for which to create packages for