example how to add library dependencies

*Hi @opsxcq!*

my goal is to build the firmware in the ci pipeline. My sketch for an ESP8266 uses libraries. 
**Could you please add an example how, to add libraries and set the board correctly?**

*I have found two files:*
```
/Applications/Arduino.app/Contents/Java/hardware/arduino/avr/boards.txt
/Applications/Arduino.app/Contents/Java/lib/version.txt
```

kind regards, André