Document ESRI projection config.

README.md

@@ -428,6 +428,7 @@ Yahoo BOSS is **not a free service**. As of November 17, 2012 Yahoo no longer of
 * **Documentation**: http://resources.arcgis.com/en/help/arcgis-online-geocoding-rest-api/
 * **Terms of Service**: http://www.esri.com/software/arcgis/arcgisonline/services/geoservices
 * **Limitations**: ?
+* **Notes**: You can specify which projection you want to use by setting, for example: `Geocoder.configure(:esri => {:outSR => 102100})`.
 
 
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