adding tutorials and example interfaces installation to README

Dockerfile

@@ -12,8 +12,7 @@ RUN source /opt/ros/${ROS_DISTRO}/setup.bash
 RUN apt-get update
 RUN rosdep update && rosdep install --from-paths src --ignore-src -r -y
 RUN if [ "$ROS_DISTRO" = "foxy" ] || [ "$ROS_DISTRO" = "galactic" ] || [ "$ROS_DISTRO" = "rolling" ]; then \
-    apt install -y ros-$ROS_DISTRO-example-interfaces \
-                   ros-$ROS_DISTRO-action-tutorials-interfaces; \
+    apt install -y ros-$ROS_DISTRO-action-tutorials-interfaces ros-$ROS_DISTRO-example-interfaces; \
     fi
 
 # colcon the ws

README.md

@@ -53,6 +53,12 @@ $ cd ~/ros2_ws
 $ colcon build
 ```
 
+If you are using a deprecated ROS 2 distro (like Foxy or Galactic) or the Rolling distro, you have to install the tutorials and example interfaces:
+
+```shell
+$ sudo apt install -y ros-$ROS_DISTRO-action-tutorials-interfaces ros-$ROS_DISTRO-example-interfaces
+```
+
 ## Docker
 
 If your operating system doesn't support ROS 2, docker is a great alternative. You can use an image from [Dockerhub](https://hub.docker.com/r/mgons/yasmin/) or create your own images. First of all, to build the image you have to use the following command: