Convert vendor imports to git instructions

[imp]

Test Plan

This is my first major doc contribution...

[rpokala]

documentation/content/en/books/developers-handbook/policies/chapter.adoc

83–97

When not referring to the git command itself, consistently use either "git" or "Git".

[emaste]

documentation/content/en/books/developers-handbook/policies/chapter.adoc

80–81

Certainly reasonable to replace svn docs with git docs, but perhaps as a second step we ought to move this with the rest of the git docs.

87–88

Just "and are visible by default." maybe

I think the "prior drafts" could be a note/caution or just something we follow up with email; most folks will read this for the first time and there's no prior draft of this doc in this form (in dev handbook).

199

We might want to suggest pushing the changes somewhere (e.g. a GitHub fork) for review, as a later change

202

Explicit branch name? git push freebsd main

204

We should probably reference "The conventional approach in FreeBSD is..." instead of or in addition to "easiest", there may be more than one way to do it, but we should have an explicit recommendation IMO.

[imp]

documentation/content/en/books/developers-handbook/policies/chapter.adoc

80–81

should be replaced by a reference. And the previous policy likely needs to be tweaked to be less prescriptive. But another day.

83–97

yea, git is the command Git is the whole system...

87–88

Tweaked. I think we can just dropped the prior drafts thing. We've had over a week to transition.

199

sure, here and below.

[imp]

review changes

[imp]

I've pushed these changes to github to test the rendering... https://github.com/bsdimp/freebsd-doc/blob/git/documentation/content/en/books/developers-handbook/policies/chapter.adoc