Architecture.md

[TechSupportJosh]

Is your feature request related to a problem? Please describe.
For new people contributing, trying to find where to make changes and where functions are is often confusing.

Describe the solution you'd like
We can add an architecture.md document to the root of this repo. We'd likely need it split into 2 parts, one for the building of Netkit and another for how Netkit actually runs.

While our project is not massive, the documentation of it will ensure people will continue to make changes in the future.

See https://matklad.github.io//2021/02/06/ARCHITECTURE.md.html