Adds docs for enabling I2C on Hass.io (#8144)

* Create enable_i2c.markdown

* Update sensor.bme680.markdown

* Update hassio_navigation.html

* ✏️ Tweaks

* ✏️ Tweaks

source/_components/sensor.bme680.markdown

@@ -13,7 +13,6 @@ ha_release: 0.62
 ha_iot_class: "Local Push"
 ---
 
-
 The `bme680` sensor platform allows you to read temperature, humidity, pressure and gas resistance values of a [Bosch BME680 Environmental sensor](https://cdn-shop.adafruit.com/product-files/3660/BME680.pdf) connected via an [I2C](https://en.wikipedia.org/wiki/I²C) bus (SDA, SCL pins). It allows you to use all the operation modes of the sensor described in its datasheet. In addition, it includes a basic air quality calculation that uses gas resistance and humidity measurements to calculate a percentage based air quality measurement.
 
 Tested devices:
@@ -186,6 +185,10 @@ group:
       - sensor.bme680_sensor_air_quality
 ```
 
+## {% linkable_title Directions for enabling I2C interface on Hass.io %}
+
+Follow the instructions here to [enable I2C on Hass.io.](/hassio/enable_i2c/).
+
 ## {% linkable_title Directions for installing SMBus support on Raspberry Pi %}
 
 Enable I2C interface with the Raspberry Pi configuration utility:

source/_includes/asides/hassio_navigation.html

@@ -19,6 +19,7 @@
           <li>{% active_link /hassio/zwave/ Z-Wave %}</li>
           <li>{% active_link /hassio/external_storage/ External storage %}</li>
           <li>{% active_link /hassio/run_local/ Execute local things %}</li>
+          <li>{% active_link /hassio/enable_i2c/ Enable I2C %}</li>
         </ul>
       </li>
     </ul>

source/hassio/enable_i2c.markdown

@@ -0,0 +1,51 @@
+---
+layout: page
+title: "Enable HassOS i2c"
+description: "Instructions on how to enable I2C on a Raspberry PI for Hass.io."
+date: 2018-01-11 20:08
+sidebar: true
+comments: false
+sharing: true
+footer: true
+---
+
+Hass.io is a managed environment, which means you can't use existing methods to enable the I2C bus on a Raspberry Pi.
+
+If you're attempting to add an external sensor, you will have to [enable the I2C interface in the Hass.io configuration](https://github.com/home-assistant/hassos/blob/dev/Documentation/boards/raspberrypi.md#i2c) using a USB stick.
+
+## {% linkable_title Step by step instructions %}
+
+You will need:
+
+- USB drive
+- A way to add files to the USB drive
+- A way to connect the drive to your Raspberry Pi
+
+### {% linkable_title Step 1 - Prepare the USB drive %}
+
+Connect the USB drive to a device capable of adding and editing files to the USB drive.
+
+Format a USB stick with FAT32/EXT4/NTFS and name the drive `CONFIG` (uppercase).
+
+### {% linkable_title Step 2 - Add files to enable I2C %}
+
+- In the root of the USB drive add a folder called `/modules`.
+- Inside that folder add a text file called `rpi-i2c.conf` with the following contents:
+  ```
+  i2c-bcm2708
+  i2c-dev
+  ```
+- In the root of the USB drive add a file called `config.txt` with the following contents:
+  ```
+  dtparam=i2c1=on 
+  dtparam=i2c_arm=on
+  ```
+
+### {% linkable_title Step 3 - Load the new USB config %}
+
+- Insert the USB drive into your Raspberry PI.
+- Now go to your Home Assistant web interface, in the sidebar click **Hass.io** > **System**.
+- Now click `Import from USB`.
+- This will restart your Hass.io instance, and load the new USB configuration.
+
+When the service has restarted, you will have a working I2C interface.