nix-shell file for easy/portable SH84

[mprimi]

Sharing my shell.nix for a self-contained SH84 setup that does not write any file outside of the repository root.

If people think there's value, I could submit this as PR (so that nixers can enter SH84 with a simple git checkout ... && nix-shell).
Also interested in hearing people's suggestions for improvements (I ain't exactly a nix master!).

{ pkgs ? import <nixpkgs> {} }:
  pkgs.mkShell {
    nativeBuildInputs = [
      pkgs.buildPackages.go
      pkgs.buildPackages.ipfs
    ];
    shellHook = ''
      # Store Go dependencies, IPFS node data, SH84 data and config
      # in this same folder rather than somewhere in HOME.
      export GOPATH=$PWD/.go
      export IPFS_PATH=$PWD/.ipfs-sh84
      export XDG_CACHE_HOME=$PWD/.xdg-cache
      export XDG_CONFIG_HOME=$PWD/.config
      # If IPFS is killing your router, setting this to false may help
      # See: https://github.com/mrusme/superhighway84/issues/14
      export ALLOW_QUIC_TRANSPORT=true

      echo "✅ Set environment:"
      echo "GOPATH=$GOPATH"
      echo "IPFS_PATH=$IPFS_PATH"
      echo "XDG_CACHE_HOME=$XDG_CACHE_HOME"
      echo "ALLOW_QUIC_TRANSPORT=$ALLOW_QUIC_TRANSPORT"
      echo "XDG_CONFIG_HOME=$XDG_CONFIG_HOME"

      echo "⏳  Building..."
      go build .

      # Bump (or reduce) file limit to a reasonable number for this shell
      ulimit -n 4096

      echo "⏳  IPFS init..."
      ipfs init
      ipfs config --json Swarm.Transports.Network.QUIC $ALLOW_QUIC_TRANSPORT

      echo "✅ Ready"
    '';
}

[mrusme]

I'm not using nix-shell but I believe it could be valuable to anyone who is. Feel free to PR! :)