Add instructions for installing using nix (#39)

akshatagarwl · web-flow · commit 9c315bef8f9e · 2021-02-17T11:35:58.000+03:00
diff --git a/docs/installation.md b/docs/installation.md
@@ -40,6 +40,12 @@ $ trizen -S dotenv-linter-bin
 $ trizen -S dotenv-linter-git
 ```
 
+#### NixOS / Nix
+
+```bash
+$ nix-env -iA nixpkgs.dotenv-linter
+```
+
 #### Windows / Scoop
 
 ```bash
