Document how Jr integration works

I haven't looked deep into details but we want the integration to be either git subtree or submodule based (or if there's a simpler option feel free to suggest) so we can easily synchronize this and [Jr-client repo](https://github.com/Jasonette/Jr-client).

If it's already implemented, need to document this. If not, need to do so.

Start by inspecting how the JEM repository currently relates to the linked Jr-client repository; the issue names git subtree and submodule as possible synchronization approaches. Determine whether an integration already exists, then document the chosen workflow or establish one if it does not. Done means contributors can follow clear instructions to synchronize both repositories.

Written by the indexing model from the issue text.