FreeBSD Handbook: fix a long note

The unusually long note at
https://github.com/freebsd/freebsd-doc/commit/a7640c82441bdf19f738af7d3b144b011750e0be?diff=unified#diff-ea68d032fa51f56f82ff87b0de858972275dc98728c98e5a8b28b6ef9640cc1cR1208-R1299
(lines 1208–1299) included a title and paragraph; a table; some
paragraphs, one of which referenced the table; then a callout list,
with number 2 referencing the same table.

The nested table at
https://docs-archive.freebsd.org/doc/11.1-RELEASE/usr/local/share/doc/freebsd/en_US.ISO8859-1/books/handbook/makeworld.html#updating-src-obtaining-src-checkout
scales well enough when the browser window is narrowed.

Nesting in the current edition of the chapter, captured at
https://web.archive.org/web/20230810000557/https://docs.freebsd.org/en/books/handbook/cutting-edge/#synching
does not scale so well.

PDF is similarly bugged; page 597 under
https://web.archive.org/web/20230813183522if_/https://download.freebsd.org/doc/en/books/handbook/handbook_en.pdf#%5B%7B%22num%22%3A4112%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22XYZ%22%7D%2C0%2C260.15%2Cnull%5D

The original note was probably intended to end after the first
paragraph – before the table. Do this now, before other changes to the
chapter.

Fixes: a7640c82441b Rewrite the Build from Source section, simplifying and clarifying.