Docs: Reintroduce overview of architecture + explanations of "hints", "components"

[padraic-shafer]

An older version of the ophyd documentation provided two sections that are no longer present (or maybe not readily discoverable).

• An overview of the architecture (model of hardware abstraction + the interface used by the bluesky RunEngine)
• An explanation of the "hints", "kind", "config", "components'.

This overview was particularly helpful to me as a newcomer to understand what problems ophyd is solving and how it does so. I'm also searching for another old version of the docs that discussed several examples of setting config and hints and signal kinds for multiple relevant applications.

I think it will be useful to reintroduce these explanation guides.

[padraic-shafer]

I'd like to submit a PR for this, but will wait until the ophyd v2 docs are removed.