Update documentation for registries

[shanmukhasampath]

Updating documentation requires all of current PRs to be approved

• [x] #175
• [x] #176
• [x] #179 and
• [x] #181.

Once they have been approved then perform the following documentation update

• [x] Birth Mother registry
• [x] Kidney registry
• [ ] Kanta registry
• [ ] concept hierarchy for non-standard codes