DOC: Update parquet docs regarding Categorical support

Fixes pandas-dev#27955

doc/source/user_guide/io.rst

@@ -4700,7 +4700,7 @@ Several caveats.
   indexes. This extra column can cause problems for non-Pandas consumers that are not expecting it. You can
   force including or omitting indexes with the ``index`` argument, regardless of the underlying engine.
 * Index level names, if specified, must be strings.
-* Categorical dtypes can be serialized to parquet, but will de-serialize as ``object`` dtype.
+* Categorical dtypes for non-string types can be serialized to parquet, but will de-serialize as ``object`` dtype.
 * Non supported types include ``Period`` and actual Python object types. These will raise a helpful error message
   on an attempt at serialization.