feat: add default sound folder guide

Author: SayanthRock

themes/default/sounds/README.md

@@ -0,0 +1,21 @@
+# Sounds
+
+Add optional theme sound files here.
+
+Recommended files:
+
+- ringtone.ogg
+- notification.ogg
+- alarm.ogg
+- ui-click.ogg
+
+## Style guide
+
+- Soft premium sound
+- Short notification tone
+- No harsh volume spike
+- Use original audio only
+
+## Customer note
+
+Sound support depends on device settings and ROM behavior. Give customers manual setup instructions if automatic setup is not supported.