Add physics write-ups to the git

[shaimach]

Is your feature request related to a problem? Please describe.
We have/are generating write-ups of relevant physics ahead of coding (e.g. non-Markovian dynamics, SU(4) structure for co-design, etc) The code isn't really understandable without this supporting material. And unless we have these in the git, putting the write-up alongside the code which implements it, we'll lose track over time.

Describe the solution you'd like
Create the write-up in whatever tool you like.
When code based on this write-up goes into the repository, so should the write-up.

Describe alternatives you've considered
Wiki. But it needs some version control that matches the code versioning.