Init: init first version of pcode-cli

Change log:
* Added the ability to display a list of all templates.
* Added the ability to download a template.
* Defined the project structure.

flake.nix

@@ -0,0 +1,60 @@
+{
+  description = "";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    {
+      nixpkgs,
+      rust-overlay,
+      flake-utils,
+      ...
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        overlays = [ (import rust-overlay) ];
+        pkgs = import nixpkgs {
+          inherit system overlays;
+        };
+      in
+      {
+        devShells.default =
+          with pkgs;
+          mkShell {
+            nativeBuildInput = with pkgs; [
+              (pkgs.rust-bin.stable.latest.default.override {
+                extensions = [
+                  "rust-src"
+                  "cargo"
+                  "rustc"
+                  "rustfmt"
+                ];
+              })
+              gcc
+            ];
+
+            RUST_SRC_PATH = "${
+              pkgs.rust-bin.stable.latest.default.override {
+                extensions = [ "rust-src" ];
+              }
+            }/lib/rustlib/src/rust/library";
+
+            buildInputs = [
+              openssl.dev
+              glib.dev
+              pkg-config
+
+              rust-analyzer
+              rustfmt
+
+              bacon
+            ];
+          };
+      }
+    );
+}