Introduce notation and clarify prerequsites

[fricklerhandwerk]

Observations
Beginners seem to struggle with some basics that may be obvious to software developers but aren't to everyone else. One example is the diff notation: #984

Problem
We're still not clear enough on what's actually required to make good use of the tutorials.

Approaches

• Introduce notation explicitly, before first use or in an index (with links to relevant resources)

• Note where appropriate that experience with Git is helpful (and link to useful materials)

  Currently the tutorials have no actual Git interaction, but Git is everywhere.

Willing to help?
As always

Priorities

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