Minor tutorial turtlesim README.md bug

[Luca Tricerri]

Describe the bug
Tutorial README.md minor:
README.md

To Reproduce

Expected behaviour
In section 8.1 Build
Instead of:

cd catkin_ws
source /opt/ros/$(ls /opt/ros)/setup.bash
source ./devel/setup.bash
catkin build alica_ros_turtlesim

use:

cd catkin_ws
source /opt/ros/$(ls /opt/ros)/setup.bash
catkin build alica_ros_turtlesim
source ./devel/setup.bash

Plans

System information (please complete the following information):

• OS: Ubuntu 20.04
• Version: rr_devel

Additional context

[Dale Koenig]

Feel free to make a PR

[Luca Tricerri]

As PR #320