Update nav2_bringup docs to include updated robot string. (#5001)

Signed-off-by: Leander Stephen D'Souza <[email protected]>

Author: leander-dsouza

nav2_bringup/README.md

@@ -25,12 +25,15 @@ This is how to launch multi-robot simulation with simple command line. Please se
 #### Cloned
 
 This allows to bring up multiple robots, cloning a single robot N times at different positions in the map. The parameter are loaded from `nav2_multirobot_params_all.yaml` file by default.
-The multiple robots that consists of name and initial pose in YAML format will be set on the command-line. The format for each robot is `robot_name={x: 0.0, y: 0.0, yaw: 0.0, roll: 0.0, pitch: 0.0, yaw: 0.0}`.
+The multiple robots that consists of name and initial pose in YAML format will be set on the command-line. The format for each robot is `{name: 'robot_name', pose: {x: 0.0, y: 0.0, z: 0.0, roll: 0.0, pitch: 0.0, yaw: 0.0}}`.
 
 Please refer to below examples.
 
 ```shell
-ros2 launch nav2_bringup cloned_multi_tb3_simulation_launch.py robots:="robot1={x: 1.0, y: 1.0, yaw: 1.5707}; robot2={x: 1.0, y: 1.0, yaw: 1.5707}"
+ros2 launch nav2_bringup cloned_multi_tb3_simulation_launch.py \
+  robots:="\
+  {name: 'robot1', pose: {x: 1.0, y: 1.0, yaw: 1.5707}}; \
+  {name: 'robot2', pose: {x: 1.0, y: 1.0, yaw: 1.5707}}"
 ```
 
 #### Unique