Medcode writeup: First pass of individual code area detail

[FairlySadPanda]

This currently outlines the folder structure for all the medcode beyond the first file.

The first pass of this is note transcription - mostly the "what this is for and how it logically works" areas. Afterward each area needs a polishing pass (which thankfully is work others can help with). See @Partmedia 's comment about wanting information about how to actually calculate how much gas, reagent or whatnot a system actually would use or need to do various things.