Added README.md for dummy_sensors (#573)

* ➕ 📖 Added README.md for dummy_sensors ROS2 package. Verified instructions.

Signed-off-by: Bey Hao Yun <[email protected]>

dummy_robot/dummy_sensors/README.md

@@ -0,0 +1,165 @@
+## **What Is This?**
+
+This demo creates and runs two ROS 2 **nodes** individually, namely `dummy_laser` and `dummy_joint_states`.
+
+**dummy_laser** publishes `sensor_msgs/msg/LaserScan` on a ROS 2 publisher topic, `/scan`.
+
+**dummy_joint_states** publishes `sensor_msgs/msg/JointState` on a ROS 2 publisher topic, `/joint_states`.
+
+Both **dummy_laser** and **dummy_joint_states** are dependencies of **dummy_robot_bringup**, and are usually expected to be run from the launch file there.
+Please refer to [dummy_robot_bringup](https://github.com/ros2/demos/tree/rolling/dummy_robot/dummy_robot_bringup).
+
+## **Build**
+
+```bash
+colcon build --packages-select dummy_sensors
+```
+
+## **Run**
+
+### **1 - dummy_laser**
+
+```bash
+ros2 run dummy_sensors dummy_laser
+```
+
+```bash
+# Terminal Output
+[INFO] [1658564972.776089023] [dummy_laser]: angle inc:	0.004363
+[INFO] [1658564972.776138078] [dummy_laser]: scan size:	1081
+[INFO] [1658564972.776148752] [dummy_laser]: scan time increment: 	0.000028
+```
+
+### **2 - dummy_joint_states**
+
+```bash
+ros2 run dummy_sensors dummy_joint_states
+```
+
+
+## **Verify**
+
+A similar terminal output should be seen after running commands described in the **Run** section above:
+
+### **1 - dummy_laser**
+
+```bash
+# Open new terminal.
+ros2 topic echo /laser
+```
+
+```bash
+# Terminal Output
+---
+header:
+  stamp:
+    sec: 1658569107
+    nanosec: 51491730
+  frame_id: single_rrbot_hokuyo_link
+angle_min: -2.356194496154785
+angle_max: 2.356194496154785
+angle_increment: 0.004363323096185923
+time_increment: 2.7777778086601757e-05
+scan_time: 0.03999999910593033
+range_min: 0.0
+range_max: 10.0
+ranges:
+- 0.39602306485176086
+- 0.39602306485176086
+- 0.39602306485176086
+- 0.39602306485176086
+- 0.39602306485176086
+- 0.39602306485176086
+- 0.39602306485176086
+- '...'
+intensities: []
+---
+```
+
+### **2 - dummy_joint_states**
+
+```bash
+# Open new terminal.
+ros2 topic echo /joint_states
+```
+
+```bash
+# Terminal Output
+---
+header:
+  stamp:
+    sec: 1658569569
+    nanosec: 414505214
+  frame_id: ''
+name:
+- single_rrbot_joint1
+- single_rrbot_joint2
+position:
+- -0.033653174530243454
+- -0.033653174530243454
+velocity: []
+effort: []
+---
+header:
+  stamp:
+    sec: 1658569569
+    nanosec: 434418040
+  frame_id: ''
+name:
+- single_rrbot_joint1
+- single_rrbot_joint2
+position:
+- -0.13326191698696957
+- -0.13326191698696957
+velocity: []
+effort: []
+---
+header:
+  stamp:
+    sec: 1658569569
+    nanosec: 454443902
+  frame_id: ''
+name:
+- single_rrbot_joint1
+- single_rrbot_joint2
+position:
+- -0.2315391504196944
+- -0.2315391504196944
+velocity: []
+effort: []
+---
+header:
+  stamp:
+    sec: 1658569569
+    nanosec: 474417706
+  frame_id: ''
+name:
+- single_rrbot_joint1
+- single_rrbot_joint2
+position:
+- -0.3275029211980919
+- -0.3275029211980919
+velocity: []
+effort: []
+---
+header:
+  stamp:
+    sec: 1658569569
+    nanosec: 494442418
+  frame_id: ''
+name:
+- single_rrbot_joint1
+- single_rrbot_joint2
+position:
+- -0.4201943910459491
+- -0.4201943910459491
+velocity: []
+effort: []
+---
+```
+
+
+## **References**
+
+- `sensor_msgs/msg/LaserScan` Message Format: https://github.com/ros2/common_interfaces/blob/rolling/sensor_msgs/msg/LaserScan.msg
+- `sensor_msgs/msg/JointState` Message Format: https://github.com/ros2/common_interfaces/blob/rolling/sensor_msgs/msg/JointState.msg