Update link to ESP8266 product page README.md (#3622)

Updates old link to ESP8266 product page which referred to a 404 page.

README.md

@@ -7,7 +7,7 @@
 
 ### A Lua based firmware for ESP8266 WiFi SOC
 
-NodeMCU is an open source [Lua](https://www.lua.org/) based firmware for the [ESP8266 WiFi SOC from Espressif](http://espressif.com/en/products/esp8266/) and uses an on-module flash-based [SPIFFS](https://github.com/pellepl/spiffs) file system. NodeMCU is implemented in C and is layered on the [Espressif NON-OS SDK](https://github.com/espressif/ESP8266_NONOS_SDK).
+NodeMCU is an open source [Lua](https://www.lua.org/) based firmware for the [ESP8266 WiFi SOC from Espressif](https://www.espressif.com/en/products/socs/esp8266) and uses an on-module flash-based [SPIFFS](https://github.com/pellepl/spiffs) file system. NodeMCU is implemented in C and is layered on the [Espressif NON-OS SDK](https://github.com/espressif/ESP8266_NONOS_SDK).
 
 The firmware was initially developed as is a companion project to the popular ESP8266-based [NodeMCU development modules]((https://github.com/nodemcu/nodemcu-devkit-v1.0)), but the project is now community-supported, and the firmware can now be run on _any_ ESP module.