Add changes in conditions of use yandex geocoding API to the README

See [this post](http://clubs.ya.ru/mapsapi/replies.xml?item_no=58741)
and also [documentation](https://tech.yandex.ru/maps/doc/geocoder/desc/concepts/input_params-docpage/) for the details

Sorry for unable to provide link to the english version.
Seems that changes are not reflected in the [english documentation](https://tech.yandex.com/maps/doc/geocoder/desc/concepts/input_params-docpage/) yet

README.md

@@ -464,9 +464,9 @@ The [Google Places Details API](https://developers.google.com/places/documentati
 
 #### Yandex (`:yandex`)
 
-* **API key**: none
+* **API key**: optional, but without it lookup is territorially limited
 * **Quota**: 25000 requests / day
-* **Region**: world
+* **Region**: world with API key. Otherwise restricted to to Russia, Ukraine, Belarus, Kazakhstan, Georgia, Abkhazia, South Ossetia, Armenia, Azerbaijan, Moldova, Turkmenistan, Tajikistan, Uzbekistan, Kyrgyzstan and Turkey
 * **SSL support**: HTTPS only
 * **Languages**: Russian, Belarusian, Ukrainian, English, Turkish (only for maps of Turkey)
 * **Documentation**: http://api.yandex.com.tr/maps/doc/intro/concepts/intro.xml