DOC: add json_normalize in See Also for read_json
I believe this should link https://pandas.pydata.org/pandas-docs/version/1.2.0/reference/api/pandas.json_normalize.html in https://pandas.pydata.org/docs/reference/api/pandas.io.json.read_json.html#pandas.io.json.read_json

`json_normalize` is great and it may help people working with JSON data who are likely to have an entry point of the `read_json` page
thanks @raybellwaves 