Add nix shell definition

.envrc

@@ -0,0 +1 @@
+use_nix

.gitignore

@@ -4,3 +4,4 @@ ui/target
 ui-sys/target
 iui/target
 target
+.direnv

shell.nix

@@ -0,0 +1,36 @@
+with import <nixpkgs> {};
+clangStdenv.mkDerivation {
+  name = "iui-nix-shell";
+  nativeBuildInputs = with pkgs; [
+    cargo
+    rustc
+    gtk3
+    pkgconfig
+  ];
+  shellHook = ''
+export LIBCLANG_PATH="${pkgs.llvmPackages_latest.libclang.lib}/lib";
+export LLVM_CONFIG_PATH="${pkgs.llvm}/bin/llvm-config";
+ export BINDGEN_EXTRA_CLANG_ARGS="$(< ${stdenv.cc}/nix-support/libc-crt1-cflags)\
+          $(< ${stdenv.cc}/nix-support/libc-cflags) \
+          $(< ${stdenv.cc}/nix-support/cc-cflags) \
+          $(< ${stdenv.cc}/nix-support/libcxx-cxxflags) \
+          ${
+            lib.optionalString stdenv.cc.isClang
+            "-idirafter ${stdenv.cc.cc}/lib/clang/${
+              lib.getVersion stdenv.cc.cc
+            }/include"
+          } \
+          ${
+            lib.optionalString stdenv.cc.isGNU
+            "-isystem ${stdenv.cc.cc}/include/c++/${
+              lib.getVersion stdenv.cc.cc
+            } -isystem ${stdenv.cc.cc}/include/c++/${
+              lib.getVersion stdenv.cc.cc
+            }/${stdenv.hostPlatform.config} -idirafter
+${stdenv.cc.cc}/lib/gcc/${stdenv.hostPlatform.config}/${
+              lib.getVersion stdenv.cc.cc
+            }/include"
+          } \
+        "
+'';
+}