Add ASN map data

This data will be used by hushd, SD and potentially other GUI clients,
so it makes the most sense for it to live here.

contrib/asmap/README.md

@@ -0,0 +1,5 @@
+# asmap stuff
+
+Files relating to -asmap=... feature, to use ASNs
+
+Originally from https://github.com/sipa/asmap/blob/master/demo.map