fix RPM build failures due to README -> README.md rename

This fixes a bug I introduced in I98e09e8900c359382e2a90b187f0c6f22a1cf81d

Change-Id: I9d7bc0aea404499315e212a2ebb92d54df85d812
diff --git a/contrib/osmo-msc.spec.in b/contrib/osmo-msc.spec.in
index 9c342f8..b5f0cd4 100644
--- a/contrib/osmo-msc.spec.in
+++ b/contrib/osmo-msc.spec.in
@@ -104,7 +104,7 @@
 
 %files
 %license COPYING
-%doc AUTHORS README
+%doc AUTHORS README.md
 %dir %{_docdir}/%{name}/examples
 %dir %{_docdir}/%{name}/examples/osmo-msc
 %{_docdir}/%{name}/examples/osmo-msc/osmo-msc.cfg