Update Cpp/cbg-executor_ping-pong/README.md

Co-Authored-By: ralph-lange <ralph-lange@users.noreply.github.com>

Author: norro

Cpp/cbg-executor_ping-pong/README.md

@@ -2,7 +2,7 @@
 
 This package provides a small example for the use of the Callback-group-level Executor concept.
 
-The Callback-group-level Executor leverages the callback-group concept in rclcpp by introducing real-time profiles such as RT-CRITICAL and BEST-EFFORT in the callback-group API (i.e. rclcpp/callback_group.hpp). Each callback requiring specific real-time guarantees, when created, may therefore be associated with a dedicated callback group. With this in place, the Executor class and depending classes (e.g., for memory allocation) were enhanced to operate at a finer, callback-group-level granularity.
+The Callback-group-level Executor leverages the callback-group concept in rclcpp by introducing real-time profiles such as RT-CRITICAL and BEST-EFFORT in the callback-group API (i.e. [rclcpp/callback_group.hpp](https://github.com/microROS/rclcpp/blob/master/rclcpp/include/rclcpp/callback_group.hpp)). Each callback requiring specific real-time guarantees, when created, may therefore be associated with a dedicated callback group. With this in place, the Executor class and depending classes (e.g., for memory allocation) were enhanced to operate at a finer, callback-group-level granularity.
 
 This allows a single node to have callbacks with different real-time profiles assigned to different Executor instances – within one process. Thus, an Executor instance can be dedicated to one or few specific callback groups and the Executor’s thread (or threads) can be prioritized according to the real-time requirements of these groups. For example, all time-critical callbacks may be handled by an "RT-CRITICAL" Executor instance running at the highest scheduler priority.