block: document zone_append_max_bytes attribute

The description of the zone_append_max_bytes sysfs queue attribute is
missing from Documentation/block/queue-sysfs.rst. Add it.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@edc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Documentation/block/queue-sysfs.rst

@@ -261,6 +261,12 @@ For block drivers that support REQ_OP_WRITE_ZEROES, the maximum number of
 bytes that can be zeroed at once. The value 0 means that REQ_OP_WRITE_ZEROES
 is not supported.
 
+zone_append_max_bytes (RO)
+--------------------------
+This is the maximum number of bytes that can be written to a sequential
+zone of a zoned block device using a zone append write operation
+(REQ_OP_ZONE_APPEND). This value is always 0 for regular block devices.
+
 zoned (RO)
 ----------
 This indicates if the device is a zoned block device and the zone model of the