Add notes on how to do a release

Author: ncw

RELEASE.md

@@ -0,0 +1,17 @@
+# Making a release #
+
+Compile and test
+
+Then run
+
+  make test_release
+
+To test the build
+
+When happy, tag the release
+
+  git tag -a 0.0XX -m "Release 0.0XX"
+
+Then do a release build (set GITHUB token first)
+
+  make release