Add text about OpenWeatherMap on README file

Author: squix78

README.md

@@ -46,26 +46,36 @@ If you are using the PlatformIO environment for building
 * adapt the [WeatherStationDemo.ino](examples/WeatherStationDemo/WeatherStationDemo.ino) file to your needs (see details above)
 
 
-## Upgrade
+## Upgrade Notes
+
+**Change to OpenWeatherMap as weather data provider**
+
+The weather information provider we used so far (Wunderground) recently stopped their free tier without previous noticeon May 15, 2018. This release adds support for a new provider with a free tier for weather information: OpenWeatherMap.com. The basic demo (WeatherStationDemo) has been adapted to use this new API through the OpenWeatherMapCurrent and OpenWeatherMapForecast REST clients. As for the previous service you'll have to acquire an API key to get access to the weather data. You can sign up for the service here: https://openweathermap.org/appid
+
+Sadly the OpenWeatherMap service has less information available in their free tier as Wunderground had. If you are missing attributes in the response constructs we are deeply sorry but don't have a better option at the moment.
+
+**ESP8266 OLED Library upgrade**
 
 The ESP8266 Oled Library changed a lot with the latest release of version 3.0.0. We fixed many bugs and improved performance and changed the API a little bit. This means that you might have to adapt your Weather Station Code if you created it using the older 2.x.x version of the library. Either compare your code to the updated WeatherStationDemo or read through the [upgrade guide](https://github.com/ThingPulse/esp8266-oled-ssd1306/blob/master/UPGRADE-3.0.md)
 
 ## Available Modules
-* **TimeClient**: simple class which uses the header date and time to set the clock
-* **NTPClient**: a NTP based time class written by Fabrice Weinberg
-* **WundergroundClient**: fetches current weather and forecast from wunderground.com
-* **ThingspeakClient**: fetches data from Thingspeak which you might have collected with another sensor node and posted there.
+* **Time Client**: simple class which uses the header date and time to set the clock
+* **NTP Client**: a NTP based time class written by Fabrice Weinberg
+* **OpenWeatherMap Client**: A REST client for the OpenWeatherMap.com service, providing weather information
+* **Aeris Client**: Client for the service provided by aerisweather.com
+* **Wunderground Client**: fetches current weather and forecast from wunderground.com. Please note: Wunderground stopped their free tier service and previous demos are now using the OpenWeatherMap client
+* **Thingspeak Client**: fetches data from Thingspeak which you might have collected with another sensor node and posted there.
 
 ## Why Weather Station as a library?
 
 I realized that more and more the Weather Station was becoming a general framework for displaying data over WiFi to one of these pretty displays. But everyone would have different ways or sources for data and having the important part of the library would rather be the classes which fetch the data then the main class.
 So if you write data fetchers which might be of interest to others please contact me to integrate them here or offer your code as extension library yourself and call it something like esp8266-weather-station-<yourservice>.
 I will gladly list it here as third party library...
-  
+
 # Changes by Lorol
 
 * Fix for [last two wrong icon entries](https://github.com/squix78/esp8266-weather-station-color/issues/39) , see [esp8266-weather-station-color](https://github.com/lorol/esp8266-weather-station-color) project fork
 * Modified WundergroundForecast and WundergroundConditions (.h and .cpp files)
-* Use #define NIGHTICONS to enable night time nt_xxxx icons processing 
+* Use #define NIGHTICONS to enable night time nt_xxxx icons processing
 
  The original README.md follows