Draft FreeBSD Git docs

These changes have been pushed into the FreeBSD tree. See the committer’s guide.

Here’s the few reamaining that didn’t fit in:

Name		Name	Last commit message	Last commit date
Latest commit History 186 Commits
README.adoc		README.adoc
SUMMARY.adoc		SUMMARY.adoc
big-picture.md		big-picture.md
design-notes.md		design-notes.md
git-how.md		git-how.md
projects-user.md		projects-user.md
pull-request.md		pull-request.md

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