Add instructions to update schema

[helen-m-lin]

Is your feature request related to a problem? Please describe.
The original specification has some validation issues, so the output is modified. The changes are tracked in schema_changes.json.
These changes need to be written back to openapi.json.

Describe the solution you'd like
Instructions in README on how to update schema in openapi.json using schema_changes.json (ideally using dictdiffer).

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Briefly tried something like this but escaped strings were being altered:

import dictdiffer
import json

with open('schema_changes.json') as f:
    schema_changes = json.load(f)
with open('openapi.json') as f:
    openapi = json.load(f)

dictdiffer.patch(schema_changes, openapi)
with open('openapi.json', 'w') as f:
    json.dump(openapi, f, indent=2)