Add C flake

c/flake.nix

@@ -0,0 +1,28 @@
+{
+  description = "C Flake";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+
+  outputs = { self, nixpkgs, flake-utils }:
+  flake-utils.lib.eachDefaultSystem
+  ( system:
+  let
+    pkgs = import nixpkgs {
+      inherit system;
+      config.allowUnfree = true;
+    };
+  in {
+    devShells.default = pkgs.mkShell {
+      packages = with pkgs; [
+        cmake
+        gcc
+        gnumake
+        valgrind
+
+        # You might want to use your own IDE.
+        jetbrains.clion
+      ];
+    };
+  });
+}