Update normalization schema in normalization.rst

[mihaitodor]

I noticed some changes were made in #466 which led to this normalization diagram being commented out from the docs. It would be very helpful to have an updated version published.

Also, I'm wondering if you can share more information on what changes need to be made to existing implementations. For example, would this one require any updates? https://github.com/biocommons/bioutils/blob/main/src/bioutils/normalize.py