Dead link to NodeMCU pin mapping

[mk-pmb]

Thanks for this great writeup! However. the link at

The ESP8266 as a microcontroller - Software Digital I/O (*) NodeMCU uses a different pin mapping, read more here.

to https://github.com/esp8266/Arduino/blob/master/doc/boards.md#nodemcu-09 is dead. Could you update it, please?