Machine learning regression feedback

reported by @erxleben in #1927 (thanks!), copying here so we don't lose track:

some additional comments:

- Fig 1 has no description of the y axis
- line 84-86: explanation of dataset content would be useful after the data upload not before
- line 188: the tool "plot actuals vs predicted curves..." is found in the statistics section. Maybe give this as a hint (most of the tools are in the ML section)
- line 226: how?
- line 253: be careful! There is a different version of the tool to be found in "Test Tools" which has different parameters. They should use the tool in the ML section
- line 317: from where does this comes from?
- Key points: a "." is missing at the end of the second key point.

Locate the machine-learning regression training material referenced by the line numbers and review the listed feedback in context. Update the figure description, dataset explanation, tool guidance, unclear explanations, warning about the Test Tools variant, source attribution, and missing punctuation. Done means each listed documentation issue is addressed in the tutorial.

Written by the indexing model from the issue text.