Add migration note containing the keepalive_count to robot_receive_ti…

…meout migration

ur_robot_driver/doc/migration/jazzy.rst

@@ -0,0 +1,10 @@
+Iron to Jazzy migration for ur_robot_driver
+===========================================
+
+keep_alive_count -> robot_receive_timeout
+-----------------------------------------
+
+Doing real-time control with a robot requires the control pc to conform to certain timing
+constraints. For this ``keep_alive_count`` was used to estimate the tolerance that was given to the
+ROS controller in terms of multiples of 20 ms. Now the timeout is directly configured using the
+``robot_receive_timeout`` parameter of the hardware interface.