Merge branch 'feature/add_readdoc_link_to_readme' into 'master'

Add readdocs link to README

See merge request sdk/ESP8266_RTOS_SDK!790

Author: donghengqaz

README.md

@@ -1,3 +1,8 @@
+# ESP8266 RTOS Software Development Kit
+
+[![Documentation Status](https://readthedocs.com/projects/espressif-esp8266-rtos-sdk/badge/?version=latest)](https://docs.espressif.com/projects/esp8266-rtos-sdk/en/latest/?badge=latest)
+
+
 # ** IMPORTANT NOTICE **
 
 ## About this repository