Get FreeBSD: title, AsciiDoc section levels

[grahamperrin]

Summary

The FreeBSD home page describes https://www.freebsd.org/where/ as 'Get FreeBSD', not 'Download FreeBSD'.

AsciiDoc: fix all section levels that fall below the section 0 (zero) title.

Fixes: 5c8cc20333c4e87dd5d3a562ad87f5c18254d5fd

Test Plan

Preview in GitHub: https://github.com/grahamperrin/freebsd-doc/blob/where-2022-11-02/website/content/en/where.adoc.

[grahamperrin]

Incidentally, the FreeBSD Handbook mentions Download FreeBSD in two places – under https://docs.freebsd.org/en/books/handbook/book/#bsdinstall-synopsis. We can aim for consistency there, and elsewhere, in separate reviews.

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For now: let's fix the section levels (my mistake in the previous review).

Whilst creating a one-and-only level 0 section for the title, I think it makes sense to have the title match what's at the home page. Forethought: yesterday's https://reviews.freebsd.org/D37235#inline-228934.

[gjb]

Approved.