nav2_core and nav2_controller short documentation (#1315)

* nav2_controller short documentation

* Added nav2_core short documentation

* minor correction indicating action server

* cleanup

nav2_controller/README.md

+# Nav2 Controller
+
+The Nav2 Controller is an [Execution Module](../doc/requirements/requirements.md) that implements the `nav2_msgs::action::FollowPath` action server.
+
+An execution module implementing the `nav2_msgs::action::FollowPath` action server is responsible for generating command velocities for the robot, given the computed path from the planner module in `nav2_planner`. The nav2_controller package is designed to be loaded with plugins for path execution. The plugins need to implement functions in the virtual base class defined in the `local_planner` header file in `nav2_core` package.
+
+
+Currently available controller plugins are: DWB, and [TEB (dashing release)](https://github.com/rst-tu-dortmund/teb_local_planner/tree/dashing-devel).
\ No newline at end of file

nav2_core/README.md

+# Nav2 Core
+
+This package hosts the abstract interface (virtual base classes) for plugins to be used with the following:
+- global planner (e.g., `nav2_navfn_planner`)
+- local planner (i.e, path execution controller, e.g `nav2_dwb_controller`)
+- goal checker
+- recovery behaviors

nav2_core/include/nav2_core/local_planner.hpp

@@ -54,7 +54,7 @@ namespace nav2_core
 
 /**
  * @class LocalPlanner
- * @brief planner interface that will be inherited by all local planners
+ * @brief planner interface that acts as a virtual base class for all local planner plugins
  */
 class LocalPlanner
 {