Spruce up BuildFromSource docs based on feedback (#26707)

* Spruce up BuildFromSource docs based on feedback

* Apply suggestions from code review

Co-authored-by: Doug Bunting <[email protected]>

* Address feedback from review

* Tweak headings for pre-reqs

* Apply suggestions from code review

Co-authored-by: Kevin Pilch <[email protected]>

* Update BuildFromSource.md

* Update docs/BuildFromSource.md

Co-authored-by: Doug Bunting <[email protected]>

Co-authored-by: Doug Bunting <[email protected]>
Co-authored-by: Kevin Pilch <[email protected]>