add field_id in doc

docs/source/cpp/parquet.rst

@@ -571,6 +571,19 @@ More specifically, Parquet C++ supports:
 * EncryptionWithFooterKey and EncryptionWithColumnKey modes.
 * Encrypted Footer and Plaintext Footer modes.
 
+Field Id
+----------
+
+The parquet format supports an optional integer field_id which can be assigned
+to a field. This is used in the `iceberg specification <https://github.com/apache/iceberg/blob/main/format/spec.md#column-projection>` __
+
+On writer side, If ``PARQUET:field_id`` is present as a metadata key on a field, and the corresponding
+value is a nonnegative integer, then it will be used as the field_id in the parquet
+file.
+
+On reader side, Arrow will convert these field IDs to a metadata key named
+``PARQUET:field_id`` on the appropriate field.
+
 Miscellaneous
 -------------