docs(geolocation): add error handling and related interfaces

src/plugins/geolocation.ts

@@ -121,14 +121,22 @@ export interface GeolocationOptions {
  * Geolocation.getCurrentPosition().then((resp) => {
  *  // resp.coords.latitude
  *  // resp.coords.longitude
- * })
+ * }).catch((error) => {
+ *   console.log('Error getting location', error);
+ * });
  *
  * let watch = Geolocation.watchPosition();
  * watch.subscribe((data) => {
+ *  // data can be a set of coordinates, or an error (if an error occurred).
  *  // data.coords.latitude
  *  // data.coords.longitude
- * })
+ * });
  * ```
+ * @interfaces
+ * Coordinates
+ * Geoposition
+ * PositionError
+ * GeolocationOptions
  */
 @Plugin({
   plugin: 'cordova-plugin-geolocation',