Added Overview section to README

Author: Matthew Hansen

README.md

@@ -2,5 +2,8 @@
 
 ROS2 Navigation
 
+# Overview
+The ROS2 Navigation system is the central control system for a robot to autonomously move to a given location on a map. Given a map and a destination, the system uses sensor input to localize the robot on the map, generates a plan to reach the destination, and outputs commands to drive a robot to that location. It will also autonomously avoid obstacles and re-plan if needed to bypass them.
+
 # Contributing
 Currently we are in the design phase, and are accepting input and requirements. To contribute, see the [design README.md](design/README.md)