Write up a high level description Learning Core

[ormsbee]

Write up a high level description of what Learning Core is, its goals, and its status. Put it in the README, and remove the old "not production ready" text.

[jmakowski1123]

From a product perspective, I'd love to hear:

Brief description of what LC is, both for technical and non-tech audience (I'm guessing linking to the ADR could cover much of the former?)
How it's different from past models
Why it's the chosen approach over blockstore, etc
What impact/benefits it has for developing new features