Complete set up of "includes" from PR 902

[mjang]

That's my intent -- see line 4.

I know you were concerned about duplicate content, and I'm trying to address that with includes, ref #902 (comment)

But you're correct that I haven't set up the include in /content/ngf/install/manifests.md yet. To minimize complexity, I'm going to set up a follow-up PR.

Originally posted by @mjang in #902 (comment)