update docs

docs/_sidebar.md

@@ -14,6 +14,7 @@
   - [Timer](timer.md)
   - [Icons](icons.md)
   - [Sounds](sounds.md)
+  - [Hidden features](dev.md)
 
 - API
   - [MQTT/HTTP](api.md)

docs/custom.md

@@ -45,4 +45,4 @@ Here's an example JSON object to display the text "Hello, AWTRIX Light!" with th
 
 ## Delete a custom app
 To delete a custom app simply send a empty payload/body to the same topic/url.
-You can also use [this API](api?id=addremove-and-rearange-apps)
+You can also use [this API](api?id=addremove-and-rearange-apps)

docs/dev.md

@@ -0,0 +1,15 @@
+# Hidden Features
+
+Ok, now they are no longer hidden :).  
+This section contains small setting options that the majority of users do not change or change very rarely and therefore saved the effort of creating an elaborate settings interface.
+
+Create a `dev.json` in your filemanager.
+
+## JSON Properties
+
+The JSON object has the following properties:
+
+| Key | Type | Description | Default |
+| --- | ---- | ----------- | ------- |
+| `bootsound` | string | Uses a custom melodie from the MELODIES folder | standart |
+| `uppercase` | boolean | Print every character in uppercase | true |

docs/onscreen.md

@@ -18,5 +18,6 @@ Hold down the middle button for 2s to exit the current menu and to save your set
 | `WEEKDAY` | Allows selection of start of week. |
 | `TEMP` | Allows selection of temperature system (°C or °F).  |
 | `APPS` | Allows to enable or disable internal apps  |
+| `SOUND` | Allows to enable or disable sound output   |
 | `UPDATE` | Check and download new firmware if available. |