nixos/manual: Re-add development section.
nixos/manual: Re-add development section.

I think this has been accidentally dropped by a099ca4, at least there is
no reason stated, why it shouldn't be included, so I'm bringing it back.

Signed-off-by: aszlig <ee1aa092358634f9c53f01b5a783726c9e21b35a@redmoonstudios.org>

NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,triton/triton,triton/triton,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,triton/triton,triton/triton,NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,NixOS/nixpkgs