afplay: add page (#3403)

pages/osx/afplay.md

@@ -0,0 +1,19 @@
+# afplay
+
+> Command-line audio player.
+
+- Play a sound file (waits until playback ends):
+
+`afplay {{path/to/file}}`
+
+- Play a sound file at 2x speed (playback rate):
+
+`afplay --rate 2 {{path/to/file}}`
+
+- Play a sound file at half speed:
+
+`afplay --rate 0.5 {{path/to/file}}`
+
+- Play the first N seconds of a sound file:
+
+`afplay --time {{seconds}} {{path/to/file}}`