tree: include nix development shell

Add a dev shell for nix environments

Signed-off-by: William Casarin <jb55@jb55.com>

shell.nix

@@ -0,0 +1,34 @@
+{ pkgs ? import <nixpkgs> {} }:
+with pkgs;
+(mkShell.override {stdenv = clangStdenv;}) {
+  buildInputs = [
+    libopus
+    libvorbis
+    opusfile
+    nlohmann_json
+    pkg-config
+    cmake
+    bzip2
+    zlib
+    SDL2
+    SDL2_net
+    spdlog
+    lsb-release
+    libpng
+    libzip
+    tinyxml-2
+
+    xorg.libX11
+    xorg.libXcursor
+    xorg.libXrandr
+    xorg.libXi
+    libglvnd
+    libxkbcommon
+  ];
+
+  #
+  # for some reason cmake needs this explicitly
+  # cmake -H. -Bbuild-cmake -GNinja -DOPUSFILE_INCLUDE_DIR=$OPUSFILE_INCLUDE_DIR
+  #
+  OPUSFILE_INCLUDE_DIR="${opusfile.dev}/include/opus";
+}