Use release helper from libosmocore

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

Change-Id: Ieb843923d8f534654413be695f2b5f0c87b75520
Related: OS#1861
diff --git a/Makefile.am b/Makefile.am
index 56cb4ba..5cf1a45 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -39,6 +39,7 @@
 	COPYING \
 	README
 
+@RELMAKE@
 
 dox: FORCE
 	doxygen doxconfig