Add attribution for MaxMind GeoLite2 to M-Lab website

MaxMind [EULA for the GeoLite2 database](https://www.maxmind.com/en/geolite2/eula) expects users to include an "attribution".

See: https://dev.maxmind.com/geoip/geolite2-free-geolocation-data/#license

```
This product includes GeoLite2 data created by MaxMind, available from
<a href="https://www.maxmind.com">https://www.maxmind.com</a>.
```