sndio: add information about alsa-sndio.

- Correct "behaviour" to en_US spelling while there.

Author: ericonr

src/config/media/sndio.md

@@ -59,10 +59,24 @@ contain a line specifying `ao=sndio`.
 ### OpenAL
 
 libopenal comes with sndio support, but prioritizes ALSA over sndio by default.
-You can configure this behaviour per user in `~/.alsoftrc` or system wide in
+You can configure this behavior per user in `~/.alsoftrc` or system wide in
 `/etc/openal/alsoft.conf` by adding the following lines:
 
 ```
 [general]
 drivers = sndio
 ```
+
+### ALSA
+
+Applications that only have an ALSA backend can still use sndio with the
+`alsa-sndio` package. It contains an ALSA plugin that provides a pcm that
+connects to a `sndiod` server, and currently only supports playback. In order to
+enable the pcm, add the lines below to your [ALSA configuration
+file](./alsa.md#configuration):
+
+```
+pcm.!default {
+	type sndio
+}
+```