Add docs for Z-Wave JS integration (#16147)

* Add docs for zwave_js integration

* Add comma

* Address review comments

* ✏️ Tweak

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

source/_integrations/zwave_js.markdown

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+---
+title: Z-Wave JS
+description: Instructions on how to integrate Z-Wave with Home Assistant via Z-Wave JS.
+ha_category:
+  - Hub
+  - Light
+  - Sensor
+ha_release: '2021.2'
+ha_iot_class: Local Push
+ha_config_flow: true
+ha_codeowners:
+  - '@home-assistant/z-wave'
+ha_domain: zwave_js
+---
+
+This integration allows you to control a Z-Wave network via Z-Wave JS.
+
+## Requirements
+
+### Core installation
+
+- The [zwave-js-server](https://github.com/zwave-js/zwave-js-server) installed and running in your network.
+
+### Hardware requirements
+
+- [Supported Z-Wave dongle](/docs/z-wave/controllers/#supported-z-wave-usb-sticks--hardware-modules). The Z-Wave controller dongle should be connected to the same host as where the Z-Wave JS server is running.
+
+## Configuration
+
+This integration can be configured using the integrations in the
+Home Assistant frontend.
+
+Menu: **Configuration** -> **Integrations**.
+
+Click on the `+` sign to add an integration and click on **Z-Wave JS**.
+After completing the configuration flow, the Z-Wave JS integration will be
+available.
+
+## Current Limitations
+
+As this integration is still in the early stages there are some important limitations to be aware of.
+
+- Platform support is currently limited to basic `sensor` and `light` entities.
+- You will need to use another tool, such as [zwavejs2mqtt](https://github.com/zwave-js/zwavejs2mqtt), to include/exclude devices and manage device configuration.