doc: edit building-node text

Simplifying some BUILDING.md and related text since a lot of people will
be reading it soon for Code & Learn. I'd prefer to delete much of this
text, but that risks controversy. These simplifications should be (I
hope) uncontroversial.

PR-URL: https://github.com/nodejs/node/pull/23335


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>