Missing dependencies when using tutorials after Debian-based install

[mjeronimo]

Using a fresh installation of Ubuntu 20.04 and following the latest instructions for a Debian-based install of ROS 2 (https://docs.ros.org/en/rolling/Installation/Ubuntu-Install-Debians.html), it is not currently possible to run through all of the tutorials in sequence, as one might expect. There are missing dependencies: colcon, colcon_cd, rosdep, etc. Perhaps there should be a section in "Configuring your ROS 2 environment" that adds any dependencies required to successfully run through the tutorials.