Add docs for network configuration (#17897)

source/_integrations/network.markdown

@@ -0,0 +1,34 @@
+---
+title: Network Configuration
+description: Network Configuration for Home Assistant
+ha_category:
+  - Other
+ha_release: 2021.6
+ha_domain: network
+ha_iot_class:
+ha_codeowners:
+  - '@home-assistant/core'
+---
+
+This integration provides network configuration for integrations such as [Zeroconf](/integrations/zeroconf/), and is managed by going to **{% my general title="Configuration >> General" %}** .
+
+**{% my general badge %}**
+
+## Auto detection
+
+Auto detection is based on the system routing next hop for the mDNS broadcast address (`224.0.0.251`).
+
+If the next-hop has non-loopback, non-link-local, non-multicast addresses, auto detection will use the interface that corresponds to the next-hop (commonly referred to as the default interface).
+
+If the next-hop cannot be detected or is a loopback address, auto detection will use all interfaces with non-loopback, non-link-local, non-multicast addresses. 
+
+## Configuration
+
+This integration is by default enabled, unless you've disabled or removed the [`default_config:`](/integrations/default_config/) line from your configuration. If that is the case, the following example shows you how to enable this integration manually:
+
+Add the following section to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+network:
+```