add short project description

README.md

@@ -1,5 +1,19 @@
 # ESP8266 WeatherStation
 
+Compact outdoor weather station.
+
+Features:
+* Temperature
+* Humidity
+* Pressure
+* dust particles PM10 (10µm) and PM2.5 (ultrafine, 2.5µm)
+* radioactivity
+* WiFi
+* needs 5V power supply
+* opensensemap.org API
+
+CAD files (OpenSCAD) and source code included.
+
 ![Weatherstation](cad/img/weatherstation.jpg)
 
 | geiger counter and DHT22              | particle sensor and ESP8266             |