Merge pull request FirebaseExtended#131 from ed7coyne/master

Added ReadTheDocs badge.

Author: proppy

README.md

@@ -2,6 +2,8 @@
 
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 This sample shows how to call [Firebase](https://www.firebase.com/) from the [ESP8266 Arduino core](https://github.com/esp8266/Arduino).