Differentiate documentation between `shared` and `reference_package`.

The README docs in the shared repo and the reference_package repo overlap quite a bit. Also, we abandoned updating documentation in reference_package where it pertains to shared procedures etc., so it has gotten stale.

We need to better differentiate the documentation in shared from the documentation in reference_package. The reference_package documentation shouldn't really document how to use the shared Git submodule other than to refer the user to the shared documentation.

See https://github.com/crickets-and-comb/reference_package/issues/21