Update readme.rst (esp8266#7379)

ESP9266 to ESP8266

doc/esp8266wifi/readme.rst

@@ -7,7 +7,7 @@ ESP8266 is all about Wi-Fi. If you are eager to connect your new ESP8266 module
 Introduction
 ------------
 
-The `Wi-Fi library for ESP8266 <https://github.com/esp8266/Arduino/tree/master/libraries/ESP8266WiFi>`__ has been developed based on `ESP8266 SDK <https://bbs.espressif.com/viewtopic.php?f=51&t=1023>`__, using the naming conventions and overall functionality philosophy of the `Arduino WiFi library <https://www.arduino.cc/en/Reference/WiFi>`__. Over time, the wealth of Wi-Fi features ported from ESP9266 SDK to `esp8266 /
+The `Wi-Fi library for ESP8266 <https://github.com/esp8266/Arduino/tree/master/libraries/ESP8266WiFi>`__ has been developed based on `ESP8266 SDK <https://bbs.espressif.com/viewtopic.php?f=51&t=1023>`__, using the naming conventions and overall functionality philosophy of the `Arduino WiFi library <https://www.arduino.cc/en/Reference/WiFi>`__. Over time, the wealth of Wi-Fi features ported from ESP8266 SDK to `esp8266 /
 Arduino <https://github.com/esp8266/Arduino>`__ outgrew `Arduino WiFi library <https://www.arduino.cc/en/Reference/WiFi>`__ and it became apparent that we would need to provide separate documentation on what is new and extra.
 
 This documentation will walk you through several classes, methods and properties of the `ESP8266WiFi <https://github.com/esp8266/Arduino/tree/master/libraries/ESP8266WiFi>`__ library. If you are new to C++ and Arduino, don't worry. We will start from general concepts and then move to detailed description of members of each particular class including usage examples.