Tutorial: Mention tool commands that can help with the steps

[mxmehl]

In the tutorial, we do not mention the new helpful commands the REUSE helper tool offers, e.g. download or addheader.

The question is whether we should base the tutorial on those commands. On the one hand, we could explain the usage of the tool directly in the tutorial. On the other hand, we would create a dependency on the tool, so users who cannot or don't want to use the tool would be left behind.

My suggestion: Let's mention the commands used for the individual steps in separate boxes after the respective parts. For example:

• In step 1: reuse init with providing the used license GPL-3.0-or-later, and/or reuse download <license>
• In step 2, reuse addheader... for the different stages and file types.

Goal: Explain mainly the manual method and basic rationale, but show how the tool supports these steps.

[mxmehl]

We already do that since quite some time