Add page on behavior tree

Add page on behavior trees.

Author: yfliu-eng

_data/navigation.yml

@@ -362,6 +362,8 @@ wiki:
         url: /wiki/planning/planning-overview/
       - title: A* Planner Implementation Guide
         url: /wiki/planning/astar_planning_implementation_guide/
+      - title: Behavior Trees
+        url: /wiki/planning/behavior-tree/
       - title: Coverage Planner Implementation Guide
         url: /wiki/planning/coverage-planning-implementation-guide/
       - title: Resolved Rates