ESP8266 Quick Start Guide and projects: benlo.com/esp8266/esp8266QuickStart.html.
Lua 5.1 Reference Manual: lua.org/manual/5.1/.
NodeMCU Documentation: nodemcu.readthedocs.org/en/dev/en/.
ESP8266 Forum and Wiki: esp8266.com.
Programming in Lua 5.0: lua.org/pil/contents.html.