Add base servo assembly and GPIO docs

.spelling

@@ -25,4 +25,5 @@ square-ish
 70x84x20mm
 83x99x24mm
 4mm
-2.2A.
+2.2A.
+uno

content/kit/servo-assembly/_index.md

@@ -1,3 +1,21 @@
 ---
 title: Servo Assembly
 ---
+
+The servo assembly allows you to control GPIO pins, Analogue pins, and servos. It's comprised of [an arduino](https://store.arduino.cc/arduino-uno-rev3), and a [servo hat](https://learn.adafruit.com/16-channel-pwm-servo-driver/overview).
+
+![Servo Assembly](/img/kit/servo-assembly.jpg?width=30pc)
+
+## Power
+The Arduino itself is powered entirely over USB. If you wish to use servos, you'll need to supply an additional 5V through the connector on the hat from the [power board](/kit/power-board).
+
+## The servo hat
+The servo hat enables you to control up to 16 servos. It's attached to the top of the arduino, passing through its pins.
+
+
+## Designs
+The board diagrams for both the Arduino and hat are below, as long as the custom firmware on the Arduino. You do not need this information to use the board but it may be of interest to some people.
+
+- [Servo Hat Schematic](https://cdn-learn.adafruit.com/assets/assets/000/036/269/original/adafruit_products_schem.png)
+- [Arduino Uno Schematic](https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf)
+- [Firmware Source](https://github.com/sourcebots/servo-firmware)

content/kit/servo-assembly/gpio.md

@@ -0,0 +1,12 @@
+---
+title: GPIO
+---
+
+The pin layout of the servo assembly is the same as an Arduino uno.
+
+![Pin Map](https://raw.githubusercontent.com/Bouni/Arduino-Pinout/master/Arduino%20Uno%20R3%20Pinout.png?width=50pc)
+
+
+{{% notice note %}}
+The servo hat communicates using 2 of the analogue output pins (4 and 5), and so these are inaccessible.
+{{% /notice %}}