zram: update recompression documentation

zram: update recompression documentation

Emphasize usage of the `priority` parameter for recompression and explain
why `algo` parameter can lead to unexpected behavior and thus is not
recommended.

Link: https://lkml.kernel.org/r/20260311084312.1766036-5-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: gao xu <gaoxu2@honor.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>