speaker-test: add page (#14042)

Co-authored-by: Wiktor Perskawiec <git@spageektti.cc>

pages/linux/speaker-test.md

@@ -0,0 +1,21 @@
+# speaker-test
+
+> Speaker test tone generator for ALSA.
+> See also: `aplay`, `arecord`, `amixer`.
+> More information: <https://manned.org/speaker-test>.
+
+- Test the default speakers with pink noise:
+
+`speaker-test`
+
+- Test the default speakers with a sine wave:
+
+`speaker-test {{-t|--test}} sine {{-f|--frequency}} {{frequency}}`
+
+- Test the default speakers with a predefined WAV file:
+
+`speaker-test {{-t|--test}} wav`
+
+- Test the default speakers with a WAV file:
+
+`speaker-test {{-t|--test}} wav {{-w|--wavfile}} {{path/to/file}}`