readme: documentation for api.targets config

README.md

@@ -45,6 +45,7 @@ The API recognizes the following properties under the top-level `api` key in you
 |`accessLog`|*no*||name of the format to use for access logs; may be any one of the [predefined values](https://github.com/expressjs/morgan#predefined-formats) in the `morgan` package. Defaults to `"common"`; if set to `false`, or an otherwise falsy value, disables access-logging entirely.|
 |`services`|*no*||service definitions for [point-in-polygon](https://github.com/pelias/pip-service), [libpostal](https://github.com/whosonfirst/go-whosonfirst-libpostal), [placeholder](https://github.com/pelias/placeholder), and [interpolation](https://github.com/pelias/interpolation) services.  If missing (which is not recommended), the services will not be called.|
 |`defaultParameters.focus.point.lon` <br> `defaultParameters.focus.point.lat`|no | |default coordinates for focus point
+|`targets.layers_by_source` <br> `targets.source_aliases` <br> `targets.layer_aliases`|no | |custom values for which `sources` and `layers` the API accepts ([more info](https://github.com/pelias/api/pull/1131)).
 
 A good starting configuration file includes this section (fill in the service and Elasticsearch hosts as needed):