Document use cases for scopes and modes

Understanding scopes is kind of hard, so we should write down as many slightly different use cases we can think of to provide a reference of ficus scope-design patterns. Here's a few, but we should have more, and nicely include them in generated docs.

## 1. One software running on multiple computers

One scope: `hostname` to have different settings based on computer, for instance
- hard drive locations (save your data to E drive)
- peripheral COM ports that are different on every computer.

## 2. SW running on multiple computers, mouse-specific overrides.

Two scopes: `hostname` and `subject_id`

Mouse-specific overrides could be something like stage position.

## 3. Instrument SW running on different computers with different topologies

Fancy multicomponent thing like prototome, that is composed of 1 microtome plus 0-2 lassos

Two scopes: `hostname` and `topology`
Where `topology` can be {`no_lasso`, `one_lasso`, `two_lasso`}