fix install instructions for go

[Mic92]

fixes https://github.com/Mic92/ssh-to-age/issues/12 bors merge

[bors[bot]]

Build succeeded:

• cross-build
• tests (nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-22.11.tar.gz, macos-latest)
• tests (nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-22.11.tar.gz, ubuntu-latest)
• tests (nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixpkgs-unstable.tar.gz, macos-latest)
• tests (nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixpkgs-unstable.tar.gz, ubuntu-latest)