docs - note for pxf parquet date conversion (#7483)

* docs - note for pxf parquet date conversion

* localize to system time first

gpdb-doc/markdown/pxf/hdfs_parquet.html.md.erb

@@ -50,6 +50,8 @@ To read and write Parquet primitive data types in Greenplum Database, map Parque
 | int64 | Bigint |
 | int96 | Timestamp |
 
+**Note**: When writing to Parquet, PXF localizes a `timestamp` to the current system timezone and converts it to universal time (UT) before finally converting to `int96`.
+
 
 ## <a id="profile_cet"></a>Creating the External Table