Added README.md for dummy_map_server (#572)

* ➕ 📖 Added README.md for dummy_map_server ROS2 package. Verified instructions. Signed-off-by: Bey Hao Yun <[email protected]> * Update dummy_robot/dummy_map_server/README.md Decomposed sentence into smaller sizes. Co-authored-by: Audrow Nash <[email protected]> Signed-off-by: Bey Hao Yun <[email protected]> * Update dummy_robot/dummy_map_server/README.md Reworded. Co-authored-by: Audrow Nash <[email protected]> Signed-off-by: Bey Hao Yun <[email protected]> * 🔨 Modified use of --packages-select to --packages-up-to based on feedback. Signed-off-by: Bey Hao Yun <[email protected]> * 🔨 Modified README.md further to adhere to feedback given. Signed-off-by: Bey Hao Yun <[email protected]> * 🔨 Modified README.md commands to adhere to higher cross-platform compatibility. Signed-off-by: Bey Hao Yun <[email protected]> * Update dummy_robot/dummy_map_server/README.md Co-authored-by: Audrow Nash <[email protected]> Signed-off-by: Bey Hao Yun <[email protected]> Signed-off-by: Bey Hao Yun <[email protected]> Co-authored-by: Audrow Nash <[email protected]>
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+## **What Is This?**
+
+This demo creates and runs a ROS2 **node**, `dummy_map_server`, that publishes `nav_msgs::msg::OccupancyGrid` on a ROS2 publisher topic, `/map`.
+
+**dummy_map_server** is also a dependency of **dummy_robot_bringup**.
+
+Please refer to [dummy_robot_bringup](https://github.com/ros2/demos/tree/rolling/dummy_robot/dummy_robot_bringup).
+
+## **What Is An Occupancy Grid?**
+
+An occupancy grid can be thought of as a map of an environment that has been divided into grid cells, where each grid cell is either occupied or unoccupied (in advanced applications, they can have other states, too).
+
+This map of occupied and unoccupied grid cells can be used to help a robot navigate a space, for example to drive through a room with furniture.
+
+If a robot is navigating a new room, however, there may also be grid cells that are marked as unknown, until that area is explored.
+
+These different states are often stored in the occupancy grid as integers, for example:
+
+:warning: Note that the integer within a cell is application-specific and can go beyond `-1` and `1`.
+
+![](img/occupancy_grid.png)
+`-1` represents **unknown** spaces.
+`0` represents **unoccupied** spaces.
+`1` represents **occupied** spaces.
+
+The illustration above shows an example of an occupancy grid where the **bolded integer** indicates the position of a robot with a lidar sensor mounted on top of it and the red-colored grid cells indicate an obstacle such as a wall.
+
+## **Build**
+
+```bash
+colcon build --packages-up-to dummy_map_server
+```
+
+## **Run**
+
+```bash
+ros2 run dummy_map_server dummy_map_server
+```
+
+## **Verify**
+
+A similar terminal output should be seen after running `ros2 run dummy_map_server` and the following commands:
+
+```bash
+ros2 topic echo /map
+```
+
+
+```bash
+# Terminal Output
+header:
+  stamp:
+    sec: 1658559453
+    nanosec: 308405010
+  frame_id: world
+info:
+  map_load_time:
+    sec: 0
+    nanosec: 0
+  resolution: 0.10000000149011612
+  width: 100
+  height: 100
+  origin:
+    position:
+      x: -5.0
+      y: -5.0
+      z: 0.0
+    orientation:
+      x: 0.0
+      y: 0.0
+      z: 0.0
+      w: 1.0
+data:
+- -1
+- -1
+- -1
+- -1
+- -1
+- -1
+- -1
+- -1
+- -1
+- '...'
+---
+
+```
+
+## **References**
+
+- `nav_msgs::msg::OccupancyGrid` Message Format: https://github.com/ros2/common_interfaces/blob/rolling/nav_msgs/msg/OccupancyGrid.msg 
diff --git a/dummy_robot/dummy_map_server/img/occupancy_grid.png b/dummy_robot/dummy_map_server/img/occupancy_grid.png