Started on overview and inheritance scheme.

docs/developer-guide/rosplane/controller-software-architecture.md

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+# Controller Software Architecture
+
+## Overview
+
+The controller makes use of inheritance to make the controller more modular.
+This creates a hierarchy of classes that each take on a responsiblity.
+This means that a user that modifies the controller only has to inherit from a particular class make the modifications only to the portions of the code that matter to them, and then continue to use the other parts of the controller.
+An example of this is provided in the code.
+The total energy controller exemplifies this by inheriting and only changing just a few key functions.
+The aim of this architecture is to make the developer's job easier.
+
+### Inheritance Scheme
+
+The controller starts off with the `controller_base` class.
+This contains all of the interface with ROS.
+The next layer implements a basic state machine for the controller.
+These states control which commands are happening at what time.
+An example of how this may be used is, ensuring the aircraft is at altitude before attempting major maneuvers.
+Following the state machine is the actual control scheme.
+By default we use a successive loop closure scheme.
+This layer calculates the control errors and necessary actuator deflections to track commands.
+
+