[DOC] Update JSON documentation in compatibility guide

[andygrove]

Report incorrect documentation

Location of incorrect documentation
Compatibility guide.

Describe the problems or issues found in the documentation
There has been a lot of work around JSON reads and from_json/to_json lately, and we should review/update the documentation.

Steps taken to verify documentation is incorrect
I read the existing docs and felt that they could be improved in light of recent changes.

Suggested fix for documentation
Review and update.