Use release helper from libosmocore

See
https://osmocom.org/projects/cellular-infrastructure/wiki/Make_a_new_release
for details.

Change-Id: Icdcb388ad22b0c009dac7968408d1e2504c838c1
Related: OS#1861
diff --git a/Makefile.am b/Makefile.am
index 970fbf7..1d7eaba 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -11,3 +11,5 @@
 	echo $(VERSION) > $(distdir)/.tarball-version
 
 EXTRA_DIST = git-version-gen .version README.md README.FreeBSD README.MacOSX README.Solaris
+
+@RELMAKE@