cargo: install man pages
cargo: install man pages

I thought about doing a seperate output for these, but they're tiny
compared to the size of the binary, so there's no point.

(cherry picked from commit 0489c1b4b20d13fa04e6460ead73893889ff2529)

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs