Add lawn mower entity (#1875)

Co-authored-by: Martin Hjelmare <marhje52@gmail.com>

docs/core/entity/lawn-mower.md

@@ -0,0 +1,52 @@
+---
+title: Lawn Mower Entity
+sidebar_label: Lawn Mower
+---
+
+Derive entity platforms from [`homeassistant.components.lawn_mower.LawnMowerEntity`](https://github.com/home-assistant/home-assistant/blob/master/homeassistant/components/lawn_mower/__init__.py)
+
+## Properties
+
+:::tip
+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
+| ---- | ---- | ------- | -----------
+| activity | LawnMowerActivity | **Required** | One of the activities in the LawnMowerActivity enum.
+| supported_features | int | (abstract method) | Bitmap of supported features. See below.
+
+## Activities
+
+| Activity | Description
+| ----- | -----------
+| `MOWING` | The lawn mower is currently mowing.
+| `DOCKED` | The lawn mower is done mowing and is currently docked.
+| `PAUSED` | The lawn mower was active and is now paused.
+| `ERROR` | The lawn mower encountered an error while active and needs assistance.
+
+## Supported Features
+
+Supported features are defined by using values in the `LawnMowerEntityFeature` enum
+and are combined using the bitwise or (`|`) operator.
+
+| Value          | Description                                          |
+| -------------- | ---------------------------------------------------- |
+| `START_MOWING`      | The lawn mower supports the mowing command.       |
+| `PAUSE`   | The lawn mower supports pausing the current task.                   |
+| `DOCK`    | The lawn mower supports the return to dock command.
+
+## Methods
+
+### `start_mowing` or `async_start_mowing`
+
+Start or resume the mowing task.
+
+### `dock` or `async_dock`
+
+Stop the lawn mower, return to dock.
+
+### `pause` or `async_pause`
+
+Pause the lawn mower during current operation.