Install systemd services with autotools

Change-Id: Ie4c7e81495181059d1dff1c194d52d11fb72ed03
diff --git a/contrib/systemd/Makefile.am b/contrib/systemd/Makefile.am
new file mode 100644
index 0000000..f565234
--- /dev/null
+++ b/contrib/systemd/Makefile.am
@@ -0,0 +1,5 @@
+if HAVE_SYSTEMD
+EXTRA_DIST = osmo-pcu.service
+systemdsystemunit_DATA = \
+  osmo-pcu.service
+endif