Reorganize devshells

devshells/bootstrap/nixpkgs.nix

@@ -0,0 +1,8 @@
+# A nixpkgs instance that is grabbed from the pinned nixpkgs commit in the lock file
+# This is useful to avoid using channels when using legacy nix commands
+let lock = (builtins.fromJSON (builtins.readFile ../../flake.lock)).nodes.nixpkgs.locked;
+in
+import (fetchTarball {
+  url = "https://github.com/nixos/nixpkgs/archive/${lock.rev}.tar.gz";
+  sha256 = lock.narHash;
+})

devshells/bootstrap/shell.nix

@@ -0,0 +1,7 @@
+# Shell for bootstrapping flake-enabled nix and home-manager
+{ pkgs ? (import ./nixpkgs.nix) { }, ... }:
+pkgs.mkShell {
+  # Enable experimental features without having to specify the argument
+  NIX_CONFIG = "experimental-features = nix-command flakes";
+  packages = with pkgs; [ nix home-manager git ];
+}