More or all platformio.ini options in the docs

[morio]

In took me a bit of time before I found
build.boot2
option for the platformio.ini file
Which I found here: #743

I was wondering if a list of options could be added to the:
https://arduino-pico.readthedocs.io/en/latest/platformio.html#
docs. It wouldn't even need a description of what they do, just that they exist, so someone like me would have a starting point when looking through the platform code to customize the platformio.ini file.