Update README.md

Added Docker example

README.md

@@ -45,6 +45,40 @@ When launching `rtabmap_ros`'s nodes, if you have the error `error while loading
 $ export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/ros/kinetic/lib/x86_64-linux-gnu
 ```
 
+### Docker
+
+* Install rtabmap inside an official ros docker image (example with melodic):
+    ```bash
+    $ docker pull ros:melodic-perception
+    $ docker run -it --rm --name=ros-melodic-rtabmap ros:melodic-perception
+    
+    # Indide the container:
+    $ apt update && apt install -y ros-melodic-rtabmap-ros && echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc
+    
+    # Before exiting the container, commit from another terminal on host:
+    $ docker commit ros-melodic-rtabmap ros:melodic-rtabmap
+    # exit container...
+    ```
+    * Note that we could build rtabmap from source in the container if we want latest version, following instructions below. Just make sure to do "`echo "source /catkin_ws/devel/setup.bash" >> ~/.bashrc`" in the container so that the following example can still work as is.
+
+* The following example show to launch a camera on host computer and run our pre-built rtabmap container. All examples from [RGB-D tutorial](http://wiki.ros.org/rtabmap_ros/Tutorials/HandHeldMapping) and [stereo tutorial](http://wiki.ros.org/rtabmap_ros/Tutorials/StereoHandHeldMapping) should work using rtabmap from the container instead. Launch camera on host computer (set ROS_IP as the IP used for docker):
+    ```bash
+    $ export ROS_IP=172.17.0.1 && roslaunch openni2_launch openni2.launch depth_registration:=true
+    # In another terminal, launch rtabmapviz or RVIZ. We do visualization 
+    # on host computer to avoid GPU problems with the container:
+    $ export ROS_NAMESPACE=rtabmap && rosrun rtabmap_ros rtabmapviz _frame_id:=camera_link
+    ```
+
+* Launch rtabmap from inside the container, saving the database on host `~/.ros/rtabmap.db`:
+    ```bash
+   $ docker run -it --rm \
+     --env ROS_MASTER_URI=http://172.17.0.1:11311 --env ROS_IP=172.17.0.2 \
+     -v ~/.ros:/root  \
+     ros:melodic-rtabmap \
+     roslaunch rtabmap_ros rtabmap.launch rtabmapviz:=false database_path:=/root/rtabmap.db rtabmap_args:="--delete_db_on_start"
+   ```
+
+
 ## Build from source
 This section shows how to install RTAB-Map ros-pkg on **ROS Hydro/Indigo/Jade/Kinetic/Lunar** (Catkin build). RTAB-Map works only with the PCL >=1.7, which is the default version installed with ROS Hydro/Indigo/Jade/Kinetic/Lunar (**Fuerte and Groovy are not supported**).