Add entity doc for siren platform

docs/core/entity/siren.md

@@ -0,0 +1,87 @@
+---
+title: Siren Entity
+sidebar_label: Siren
+---
+
+A siren entity is a device whose main purpose is to control siren devices like a doorbell or chime. Derive entity platforms from [`homeassistant.components.siren.SirenEntity`](https://github.com/home-assistant/home-assistant/blob/master/homeassistant/components/siren/__init__.py)
+
+## Properties
+
+> Properties should always only return information from memory and not do I/O (like network requests). Implement `update()` or `async_update()` to fetch data.
+
+| Name                    | Type   | Default                               | Description                                                                             |
+| ----------------------- | ------ | ------------------------------------- | --------------------------------------------------------------------------------------- |
+| volume_level            | float  | `None`                                | The volume level for the device.                                        |
+| active_tone             | string | `NotImplementedError()`               | The active tone for the device. Requires `SUPPORT_TONES`.                               |
+| available_tones         | list   | `NotImplementedError()`               | The available tones for the device. Requires `SUPPORT_TONES`.                           |
+| is_on                   | bool   | `NotImplementedError()`               | Whether the device is on or off.                                                        |
+
+### Tones
+
+A device can have different tones that are played. Integrations are responsible for providing the available tones when supported.
+
+### Supported features
+
+Supported features constants are combined using the bitwise or (`|`) operator.
+
+| Name                      | Description                                                    |
+| ------------------------- | -------------------------------------------------------------- |
+| `SUPPORT_TONES`           | The device supports different tones.                           |
+| `SUPPORT_VOLUME_SET`      | The device supports setting the volume level of the device.    |
+
+
+## Methods
+
+### Set volume level
+
+```python
+class MySirenEntity(SirenEntity):
+    # Implement one of these methods.
+
+    def set_volume_level(self, volume_level: float):
+        """Set new volume level."""
+
+    async def async_set_volume_level(self, volume_level: float):
+        """Set new volume level."""
+```
+
+### Set active tone
+
+This should only be implemented if the tone can be changed.
+
+```python
+class MySirenEntity(SirenEntity):
+    # Implement one of these methods.
+
+    def set_active_tone(self, tone: str):
+        """Set new active tone."""
+
+    async def async_set_active_tone(self, tone: str):
+        """Set new active tone."""
+```
+
+### Turn on
+
+```python
+class MySirenEntity(SirenEntity):
+    # Implement one of these methods.
+
+    def turn_on(self, **kwargs):
+        """Turn the device on."""
+
+    async def async_turn_on(self, **kwargs):
+        """Turn the device on."""
+```
+
+### Turn off
+
+```python
+class MySirenEntity(SirenEntity):
+    # Implement one of these methods.
+
+    def turn_off(self, **kwargs):
+        """Turn the device off."""
+
+    async def async_turn_off(self, **kwargs):
+        """Turn the device off."""
+```