examples: fix shell on non-Linux systems

extra-container is not supported on these systems.

Also mention that VM examples require Linux.

examples/README.md

@@ -18,11 +18,11 @@ By default, [`configuration.nix`](configuration.nix) enables `bitcoind` and `cli
   Requires: [Nix](https://nixos.org/), a systemd-based Linux distro and root privileges
 
 - [`./deploy-qemu-vm.sh`](deploy-qemu-vm.sh) creates a QEMU VM.\
-  Requires: [Nix](https://nixos.org/nix/)
+  Requires: [Nix](https://nixos.org/nix/), Linux
 
 - [`./deploy-krops.sh`](deploy-krops.sh) creates a QEMU VM and deploys a
   nix-bitcoin configuration to it using [krops](https://github.com/krebs/krops).\
-  Requires: [Nix](https://nixos.org/nix/)
+  Requires: [Nix](https://nixos.org/nix/), Linux
 
 - [`./deploy-container-minimal.sh`](deploy-container-minimal.sh) creates a
   container defined by [minimal-configuration.nix](minimal-configuration.nix) that

helper/makeShell.nix

@@ -1,20 +1,20 @@
 { configDir, shellVersion ? null, extraShellInitCmds ? (pkgs: "") }:
 let
+  inherit (pkgs) lib;
   nixpkgs = (import ../pkgs/nixpkgs-pinned.nix).nixpkgs;
   pkgs = import nixpkgs {};
   nbPkgs = import ../pkgs { inherit pkgs; };
   cfgDir = toString configDir;
+  path = lib.optionalString pkgs.stdenv.isLinux ''
+    export PATH="${lib.makeBinPath [ nbPkgs.extra-container ]}''${PATH:+:}$PATH"
+  '';
 in
-with pkgs;
+pkgs.stdenv.mkDerivation {
-stdenv.mkDerivation rec {
   name = "nix-bitcoin-environment";
 
-  path = lib.makeBinPath [ nbPkgs.extra-container ];
-
   shellHook = ''
     export NIX_PATH="nixpkgs=${nixpkgs}:nix-bitcoin=${toString ../.}:."
-    export PATH="${path}''${PATH:+:}$PATH"
+    ${path}
-
     export NIX_BITCOIN_EXAMPLES_DIR="${cfgDir}"
 
     # Set isInteractive=1 if
@@ -111,7 +111,7 @@ stdenv.mkDerivation rec {
     }
 
     if [[ $isInteractive ]]; then
-      ${figlet}/bin/figlet "nix-bitcoin"
+      ${pkgs.figlet}/bin/figlet "nix-bitcoin"
       echo 'Enter "h" or "help" for documentation.'
     fi