aplay: add a paragraph for '--samples' ('-s') option to aplay manual

aplay: add a paragraph for '--samples' ('-s') option to aplay manual

A '--samples' ('-s') option was added so that record/playback process is
terminated after handling the same number of PCM frames as a value of the
option. However this option is not described in aplay manual.

This commit adds a paragraph for the option.

Fixes: 3d44e2bc159e ('aplay: Add samples argument for playing/recording a given number of samples')
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Reviewed-by: Daniel Baluta daniel.baluta@nxp.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>