Adding nix flake for development to project

.env

@@ -0,0 +1,2 @@
+# Add environment variables here to be available in development session.
+# Example: export SECRET_TOKEN=01234

README.md

@@ -118,3 +118,92 @@ fcidr 10.0.0.0/8 + 127.0.0.0/16 | fcidr - 10.64.0.0/16 | fcidr !
 127.128.0.0/9
 128.0.0.0/1
 ```
+
+### Development
+
+#### Prerequisites
+
+- [nix](https://nixos.org/download.html)
+- [nix flakes](https://nixos.wiki/wiki/Flakes#Enable_flakes)
+
+#### How-to
+
+Create the development shell environment. Necessary to run all other commands.
+
+```shell
+nix develop
+```
+
+Build with cargo.
+
+```shell
+just build
+```
+
+Check the code with cargo's built-in fast static analysis.
+
+```shell
+just check
+```
+
+Remove build files.
+
+```shell
+just clean
+```
+
+Format the code.
+
+```shell
+just format
+```
+
+Check the code with clippy for better static analysis.
+
+```shell
+just lint
+```
+
+Run the application.
+
+```shell
+just run
+```
+
+Run tests with cargo's built-in test runner.
+
+```shell
+just test
+```
+
+Watch for code changes and rebuild.
+
+```shell
+just watch
+```
+
+All `just` commands can accept additional command line arguments after a `--`.
+
+For example: run the application with a flag to report the version.
+
+```shell
+just run -- --version
+```
+
+##### Tips and Recommendations
+
+###### Open IDE from Development Shell
+
+To get linking to rust binaries in your IDE, you should open the development shell from your terminal and then open your IDE
+from that shell session. This will carry over the development shell's environment into your IDE.
+
+For example if you work with VSCode.
+
+```shell
+cd path/to/this/project
+nix develop
+code .
+```
+
+By doing this, you can install the rust-analyzer VSCode extension and it will work properly since it will be able to point to
+the correct rust binaries and libraries. You will also have access in VSCode to any packages installed by the nix flake.

flake.nix

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+{
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      pkgs = nixpkgs.legacyPackages.${system};
+    in {
+      devShell = pkgs.mkShell {
+        buildInputs = [
+          pkgs.cargo-watch
+          pkgs.iconv
+          pkgs.just
+          pkgs.nerdfonts
+          pkgs.rustup
+          pkgs.starship
+        ];
+        shellHook = ''
+          source .env
+          rustup default stable
+          eval "$(starship init bash)"
+        '';
+      };
+    });
+}

justfile

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+build *ARGS:
+  cargo build {{ARGS}}
+
+check *ARGS:
+  cargo check {{ARGS}}
+
+clean *ARGS:
+  cargo clean {{ARGS}}
+
+format *ARGS:
+  cargo format {{ARGS}}
+
+lint *ARGS:
+  cargo lint {{ARGS}}
+
+run *ARGS:
+  cargo run {{ARGS}}
+
+test *ARGS:
+  cargo test {{ARGS}}
+
+watch *ARGS:
+  cargo watch {{ARGS}}