docs: add info about installation via Nix

Signed-off-by: Nikolai Mishin <sanduku.default@gmail.com>

README.md

@@ -148,30 +148,45 @@ sudo dpkg -i cosign_${LATEST_VERSION}_amd64.deb
 
 <a id="automatic-installation"></a>
 #### Automatic Installation
-<details><summary><b>Arch Linux (AUR)</b></summary><br>
+<details><summary><b>Arch Linux (AUR, Nix)</b></summary><br>
 
 This package is available on the Arch Linux User Repository.
 It can be installed using the yay AUR helper:
 ```sh
 yay tenv-bin
 ```
 
+Installation via Nix package manager:
+```sh
+nix-env -i tenv
+```
+
 </details>
 
-<details><summary><b>MacOS (Homebrew)</b></summary><br>
+<details><summary><b>MacOS (Homebrew, Nix)</b></summary><br>
 
 ```console
 brew install tenv
 ```
 
+Installation via Nix package manager:
+```console
+nix-env -i tenv
+```
+
 </details>
 
-<details><summary><b>Windows (Chocolatey)</b></summary><br>
+<details><summary><b>Windows (Chocolatey, Nix)</b></summary><br>
 
 ```console
 choco install tenv
 ```
 
+Installation via Nix package manager:
+```console
+nix-env -i tenv
+```
+
 </details>
 
 <details><summary><b>Ubuntu</b></summary><br>
@@ -182,6 +197,11 @@ curl -O -L "https://github.com/tofuutils/tenv/releases/latest/download/tenv_${LA
 sudo dpkg -i "tenv_${LATEST_VERSION}_amd64.deb"
 ```
 
+Installation via Nix package manager:
+```console
+nix-env -i tenv
+```
+
 </details>