[skip-ci] Add clarifying comment

infrastructure/docker-federated/image/Dockerfile

@@ -28,6 +28,7 @@ RUN if [ -n "${GITEA_VERSION}" ]; then git checkout "${GITEA_VERSION}"; fi \
 # Begin env-to-ini build
 RUN go build contrib/environment-to-ini/environment-to-ini.go
 
+# Run stage
 FROM docker.io/library/alpine:3.17
 LABEL maintainer="contact@forgejo.org"