Use some PRs for narrative documentation on contribution #1084

📚 New content request

Add narrative documentation describing how to implement things both into napari's architecture and accomodating for our own implementation details. High value things to touch on include:

1. Relationship between Vispy, Models, and Qt
2. How to add to preferences and actions/app-model (and when for each)
3. How to account for multiscale and async (and RGB)

Outline

1. Big Histogram PR explanation Histogram for the Image layer controls and contrast limits popup napari#8391 (vispy, model, qt, multiscale, async, progressive, remote)
2. Camera syncing Toggleable synced (default) and separated camera views across ndisplay napari#9151 (settings, app-model, models, passing between Qt and Vispy, popup contribution)