Updated diagnostics architecture description (#285)

* Improved uros diagnostic architecture diagram
* Mention necessary translation of diagnostic messages
* Update _docs/concepts/client_library/diagnostics/index.md

Signed-off-by: Arne Nordmann (CR/AEA2) <arne.nordmann@de.bosch.com>
Co-authored-by: Ralph Lange <ralph-lange@users.noreply.github.com>

Author: norro

_docs/concepts/client_library/diagnostics/diagnostics_architecture.png

@@ -5,14 +5,16 @@ permalink: /docs/concepts/client_library/diagnostics/
 
 Although diagnostics is not part of the ROS 2 Client Library packages (i.e., rclcpp, rclpy), it definitely can be counted to the extended client library as it provides very generic and application-independent functionalities.
 
-That's why the micro-ROS Client Library also comes with basic diagnostics functionalities. These are compatible with ROS 2 diagnostics, but comprise three features only:
+That's why the micro-ROS Client Library comes with basic diagnostics functionalities. These are compatible with ROS 2 diagnostics and comprise three features only:
 
 * Diagnostic message types (optimized for Micro-XRCE-DDS - no dynamic arrays)
 * Updater mechanisms for rclc
-* Selected basic diagnostic monitors
+* Selected basic diagnostic monitors for microcontrollers
 
-The micro-ROS diagnostics packages do not provide any aggregation mechanisms as we assume that such aggregation takes place on a microprocessor running standard ROS 2. Hence, we assume the following typical architecture:
+The micro-ROS diagnostics packages do not provide any aggregator as we assume that such aggregation takes place on a microprocessor running standard ROS 2. Hence, we assume the following typical architecture:
 
 <img src="diagnostics_architecture.png" style="display:block; width:60%; margin-left:auto; margin-right:auto;"/>
 
-For more information, please see [https://github.com/micro-ROS/micro_ros_diagnostics/](https://github.com/micro-ROS/micro_ros_diagnostics/).
+In order for the standard ROS 2 diagnostic aggregator to aggregate micro-ROS diagnostic message types, the ROS 2 agent has to translate micro-ROS diagnostic messages to standard ROS 2 diagnostic messages (*tbd*).
+
+For more information, please see [https://github.com/micro-ROS/micro_ros_diagnostics/](https://github.com/micro-ROS/micro_ros_diagnostics/). For further information on ROS 2 diagnostics, see [ROS 2 diagnostics](https://github.com/ros/diagnostics/tree/ros2-devel) and [ROS 2 diagnostic_msgs](https://github.com/ros2/common_interfaces/tree/master/diagnostic_msgs).