Find a new home for Copying Closures via SSH

[fricklerhandwerk]

Copying Closures via SSH should be removed from the Nix manual according to NixOS/nix#7769, as this is clearly a guide.

We want to keep the information, because it appears to be a fairly well-known use case.
Currently nix.dev doesn't have a dedicated section for guides, but this may be an opportunity to open one.

[eflanagan0]

It seems like nix.dev does have a good place for guides like this today:

• source/guides/recipes/

Subjectively, I am a frequent user of nix-copy-closure so am happy to contribute porting the recipe and cleaning it up according to the standards established in the guide on how to guides. (See #977).

notes

• address real-world complexity of PATH troubles on non-NixOS installations of nix
  • nix-copy-closure: support non-NixOS machines nix#1078

[fricklerhandwerk]

@eflanagan0 that would be great! Feel free to drop into the documentation office hours if you want to hack on it together or discuss progress.