* Nix: update and add documentation for nix subcommands
Updates the documentation on the new unstable Nix command & subcommands,
and adds a separate page for the Classic Nix commands.
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Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: axtloss <axtlos@getcryst.al>
Co-authored-by: CleanMachine1 <78213164+CleanMachine1@users.noreply.github.com>
