Add a link to the OSM Geocoding Guidelines

Author: orangejulius

public/attribution.md

@@ -1,7 +1,7 @@
 ## Attribution
 * Geocoding by [Pelias](https://pelias.io).
 * Data from
-   * [OpenStreetMap](http://www.openstreetmap.org/copyright) © OpenStreetMap contributors under [ODbL](http://opendatacommons.org/licenses/odbl/)
+   * [OpenStreetMap](http://www.openstreetmap.org/copyright) © OpenStreetMap contributors under [ODbL](http://opendatacommons.org/licenses/odbl/). Also see the [OSM Geocoding Guidelines](https://wiki.osmfoundation.org/wiki/Licence/Community_Guidelines/Geocoding_-_Guideline) for acceptable use.
    * [OpenAddresses](http://openaddresses.io) under [various public-domain and share-alike licenses](http://results.openaddresses.io/)
    * [GeoNames](http://www.geonames.org/) under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/)
    * [WhosOnFirst](https://www.whosonfirst.org/) under [various CC-BY or CC-0 equivalent licenses](https://whosonfirst.org/docs/licenses/)