Added general node documentation

electrical/documents/nodes/readme.md

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+## Hardware Node Documentation
+
+This page describes the hardware nodes that are present for the 1718 Mars Rover project.
+
+The project contains the following nodes:
+
+- [IRIS](#iris-node)
+- [Motor](#motor-node)
+- Tower
+- Pan-Tilt
+- Grasping
+- Science
+- Arm Breakout 1 / 2
+
+### IRIS node
+
+<img src="files/iris.jpg" width="300">
+
+This node serves as the computer's main interface with the hardware in the rest of the Rover. It features 10 RS485 ports and a Teensy Microcontroller that allows it to perform most of the control and sensing features for the Rover.
+
+[Find more documentation here.](iris.md)
+
+### Motor node
+
+<img src="files/motor_render.png" width="300">
+
+This node controls the motors that turn Rover's wheels.
+
+[Find more documentation here.](motor.md)