Documentation of Xiaomi Smart WiFi Socket and Power Strip component (#3248)

* Documentation for Xiaomi Smart WiFi Socket and Smart Power Strip component added.

* Section "Retrieving the Access Token" has a central place now.

* Spelling & grammar fixed.

* Broken link fixed.
HA version updated.

* Component renamed: switch.xiaomi_plug -> switch.xiaomi_miio.

* Update switch.xiaomi_miio.markdown

source/_components/switch.xiaomi_miio.markdown

@@ -0,0 +1,36 @@
+---
+layout: page
+title: "Xiaomi Smart WiFi Socket and Smart Power Strip"
+description: "Instructions how to integrate your Xiaomi Smart WiFi Socket aka Plug or Xiaomi Smart Power Strip within Home Assistant."
+date: 2017-08-26 10:18
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: xiaomi.png
+ha_category: Switch
+ha_version: 0.56
+ha_iot_class: "Local Polling"
+---
+
+The `xiaomi_miio` switch platform allows you to control the state of your Xiaomi Smart WiFi Socket aka Plug or Xiaomi Smart Power Strip.
+
+Currently, the supported features are `on`, `off`. If the device provides the current load, it will be reported.
+
+Please follow the instructions on [Retrieving the Access Token](/components/vacuum.xiaomi/#retrieving-the-access-token) to get the API token to use in the `configuration.yaml` file.
+
+To add a plug to your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entries
+switch:
+  - platform: xiaomi_miio
+    name: Original Xiaomi Mi Smart WiFi Socket
+    host: 192.168.130.59
+    token: YOUR_TOKEN
+```
+
+Configuration variables:
+- **host** (*Required*): The IP of your plug.
+- **token** (*Required*): The API token of your plug.
+- **name** (*Optional*): The name of your plug.