add labels with git commit and author for docker images

Makefile

@@ -5,8 +5,16 @@ deps:
 test:
 	go test ./...
 
+image: AUTHOR = $(shell echo $$USER)
+image: GIT_COMMIT = $(shell tag=`git describe --exact-match --tag 2>/dev/null`; \
+	if [ $$? -eq 0 ]; then echo $$tag | sed 's/^v\(.*\)$$/\1/'; \
+	else git rev-parse --short HEAD; fi)
 image:
-	docker build . -t statusteam/rendezvous:latest
+	docker build . \
+		--label "commit=$(GIT_COMMIT)" \
+		--label "author=$(AUTHOR)" \
+		-t statusteam/rendezvous:$(GIT_COMMIT)
+		-t statusteam/rendezvous:latest
 
 push:
 	docker push statusteam/rendezvous:latest