Rework subsection headers of the Motivation section

[dokempf]

There is currently a mismatch between the subsection headers and their content.

Google Doc comments referring to this:
At the moment, the text for this subsection does not reflect the heading. Only training is mentioned in terms of tasks and "only" examples are given, no actual arguments to the question "why".

I find the hierarchy of headings a bit confusing (throughout the document). I assume this is because it's not really been consolidated? This is not a sub-chapter of "Motivation", for instance, is it?
Also, I understand that the "motivation" section explains the motivation for writing the position paper, not the motivation for having central RSE. But then maybe the naming of the "motivation" section could be clarified? And I have difficulties in seeing whether the motivation for having central RSE is just explained throughout the rest of the document or whether it is meant to be concentrated in some particular section (e.g. "Benefits").

(refering to Why do central services make sense?)
This question, as posed, is not clear: do we mean "Why do software services make sense" or "Why does it make sense for the services to be central" or "both?" Regardless, those should be answered separately.

[dokempf]

I would like to emphasize the importance of this moving forward. I think it is the last structural issue that we have.