docs: add nix setup instructions

CONTRIBUTING.md

@@ -31,6 +31,18 @@ When you submit your first pull request, you acknowledge that you agree to the t
 
 ## Development Setup
 
+### Using Nix (Recommended for Linux)
+
+If you have [Nix](https://nixos.org/) installed, you can skip the manual setup below and simply run:
+
+```bash
+nix develop
+```
+
+This will provide Node.js, Rust, and all necessary system libraries.
+
+### Manual Setup
+
 Ensure you have the following dependencies installed:
 
 - Node.js (see `.node-version` for exact version)

README.md

@@ -59,6 +59,16 @@ The app can be downloaded from the [releases page](https://github.com/zhom/donut
 
 See [CONTRIBUTING.md](CONTRIBUTING.md).
 
+### Nix Support
+
+For a reproducible development environment (especially on Linux), you can use [Nix](https://nixos.org/):
+
+```bash
+nix develop
+# or if you use direnv
+direnv allow
+```
+
 ## Issues
 
 If you face any problems while using the application, please [open an issue](https://github.com/zhom/donutbrowser/issues).