DOC: update parquet documentation categorical support

[jorisvandenbossche]

http://pandas-docs.github.io/pandas-docs-travis/io.html#parquet is a bit outdated, we should investigate a bit the current state of what support there is in pyarrow and fastparquet

[datapythonista]

I think this is superseded by #27955, should we close this?

[alimcmaster1]

Looks like this was addressed in #28018 feel free to reopen if you feel otherwise Joris

[jorisvandenbossche]

That is indeed solved! Thanks for cleaning up