docs: update README with nix setup instructions

README.md

@@ -41,6 +41,20 @@ Use an [AUR helper](https://wiki.archlinux.org/title/AUR_helpers), such as `yay`
 yay -S leaf-markdown-viewer
 ```
 
+Nix:
+
+Run without installing:
+
+```bash
+nix run github:RivoLink/leaf
+```
+
+Install into your profile:
+
+```bash
+nix profile install github:RivoLink/leaf
+```
+
 Verify the installation:
 
 ```bash
@@ -95,6 +109,28 @@ If `~/.local/bin` is not already on your `PATH`, add it to `~/.bashrc` or `~/.zs
 export PATH="$HOME/.local/bin:$PATH"
 ```
 
+### Nix
+
+Build with Nix (no Rust toolchain required on the host):
+
+```bash
+nix build
+./result/bin/leaf --version
+```
+
+Enter the development shell — it provides the Rust toolchain, `pkg-config`, `oniguruma`, `cargo-watch`, and `cargo-edit`:
+
+```bash
+nix develop
+cargo build --release
+```
+
+Run the full check suite (build + clippy + rustfmt):
+
+```bash
+nix flake check
+```
+
 ## Usage
 
 ```bash

flake.nix

@@ -0,0 +1,79 @@
+{
+  description = "leaf - A friendly terminal Markdown previewer";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    crane.url = "github:ipetkov/crane";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, crane }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+
+        craneLib = crane.mkLib pkgs;
+
+        nativeBuildInputs = with pkgs; [ pkg-config ];
+
+        # syntect's regex-onig feature requires the oniguruma C library.
+        # reqwest uses rustls-tls (pure-Rust TLS) so no Security/SystemConfiguration
+        # frameworks are needed. crossterm uses POSIX terminal APIs covered by the
+        # stdenv SDK, so no explicit darwin framework inputs are required.
+        buildInputs = with pkgs; [ oniguruma ];
+
+        commonArgs = {
+          src = craneLib.cleanCargoSource ./.;
+          strictDeps = true;
+          inherit nativeBuildInputs buildInputs;
+          # Tell the oniguruma-sys build script to link the system library.
+          RUSTONIG_SYSTEM_LIBONIG = true;
+        };
+
+        cargoArtifacts = craneLib.buildDepsOnly commonArgs;
+
+        leaf = craneLib.buildPackage (commonArgs // {
+          inherit cargoArtifacts;
+          meta = with pkgs.lib; {
+            description = "A friendly terminal Markdown previewer";
+            homepage = "https://github.com/RivoLink/leaf";
+            license = licenses.mit;
+            mainProgram = "leaf";
+            platforms = platforms.unix;
+          };
+        });
+      in
+      {
+        packages = {
+          default = leaf;
+          inherit leaf;
+        };
+
+        apps.default = flake-utils.lib.mkApp { drv = leaf; };
+
+        checks = {
+          inherit leaf;
+
+          leaf-clippy = craneLib.cargoClippy (commonArgs // {
+            inherit cargoArtifacts;
+            cargoClippyExtraArgs = "--all-targets -- --deny warnings";
+          });
+
+          leaf-fmt = craneLib.cargoFmt {
+            src = commonArgs.src;
+          };
+        };
+
+        devShells.default = craneLib.devShell {
+          checks = self.checks.${system};
+          packages = with pkgs; [
+            clippy
+            rustfmt
+            cargo-edit
+            cargo-watch
+          ];
+          RUSTONIG_SYSTEM_LIBONIG = true;
+        };
+      }
+    );
+}