Add helper script to print sha/md5 of tar files

During release, there is manual work of generating the sha and md5
values from the built tar. This PR adds the helper script to generate
those in markdown format, so that it easier and less error-prone.

Makefile

@@ -18,7 +18,8 @@
         vet fmt version test e2e-test \
         build-binaries build-container build-tar build \
         docker-builder build-in-docker \
-        push-container push-tar push release clean depup
+        push-container push-tar push release clean depup \
+        print-tar-sha-md5
 
 all: build
 
@@ -273,7 +274,10 @@ push-tar: build-tar
 push: push-container push-tar
 
 # `make release` is used when releasing a new NPD version.
-release: push-container build-tar
+release: push-container build-tar print-tar-sha-md5
+
+print-tar-sha-md5: build-tar
+	./hack/print-tar-sha-md5.sh $(VERSION)
 
 coverage.out:
 	rm -f coverage.out