add geoip2 system test

bin/tests/system/geoip2/data/README.md

@@ -0,0 +1,12 @@
+##### Test MMDB databases
+
+This directory contains test versions of the GeoIP2/GeoLite2 CIty,
+Country, Domain, ISP, and ASN databases. The `.mmdb` files are built
+from the corresponding `.json` source files; to regenerate them, modify
+the source files and run `perl write-test-data.pl`.
+
+This script is adapted from one in
+[https://github.com/maxmind/MaxMind-DB](https://github.com/maxmind/MaxMind-DB).
+It depends on the MaxMind:DB:Writer module, which can be found in
+CPAN or at
+[https://github.com/maxmind/MaxMind-DB-Writer-perl](https://github.com/maxmind/MaxMind-DB-Writer-perl) .