Add initial Sense HAT Input node

hardware/sensehat/README.md

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+node-red-node-pi-sense-hat
+==========================
+
+A <a href="http://nodered.org" target="_new">Node-RED</a> node to interact with
+a Raspberry Pi Sense HAT.
+
+## Pre-requisites
+
+The Sense HAT python drivers need to be installed manually:
+
+```
+sudo apt-get update
+sudo apt-get install sense-hat
+sudo pip-3.2 install pillow
+```
+
+See the <a href="http://pythonhosted.org/sense-hat/" target="_new">driver documentation</a>
+for more information.
+
+
+## Install
+
+Run the following command in your Node-RED user directory (typically `~/.node-red`):
+
+    npm install node-red-node-pi-sense-hat
+
+## Usage
+
+### Input Node
+
+This node sends readings from the various sensors on the Sense HAT, grouped into three sets; motion events, environment events and joystick events.
+
+#### Motion events
+
+Motion events include readings from the accelerometer, gyroscope and magnetometer,
+as well as the current compass heading. They are sent at a rate of approximately 10
+per second. The `topic` is set to `motion` and the `payload` is an object with the
+following values:
+
+  - `acceleration.x/y/z` : the acceleration intensity in Gs
+  -`gyroscope.x/y/z` : the rotational intensity in radians/s
+  -`orientation.roll/pitch/yaw` : the angle of the axis in degrees
+  -`compass` : the direction of North in degrees
+
+#### Environment events
+
+Environment events include readings from the temperature, humidity and pressure
+sensors. They are sent at a rate of approximately 1 per second.  The `topic`
+is set to `environment` and the `payload` is an object
+with the following values:
+
+  -`temperature` : degrees Celsius
+  -`humidity` : percentage of relative humidity
+  -`pressure` : Millibars
+
+#### Joystick events
+
+Joystick events are sent when the Sense HAT joystick is interacted with. The
+`topic` is set to `joystick` and the `payload` is an object with the following values:
+
+  -`key` : one of `UP`, `DOWN`, `LEFT`, `RIGHT`, `ENTER`
+  -`state` : the state of the key:
+    -`0` : the key has been released
+    -`1` : the key has been pressed
+    -`2` : the key is being held down