Add nixpkgs as distribution to docs

Author: fliiiix

docs/assets/pkg_logos/nix.png

@@ -272,6 +272,14 @@ <h3 style="text-align:center;">Crow is everywhere, you just need to grab it!<h3>
 </a>
 </div>
 
+<div class="dcard">
+<a href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/by-name/cr/crow/package.nix">
+    <img class="dcard__image" src="assets/pkg_logos/nix.png">
+    <p class="dcard__title">Nixpkgs</p>
+    <p class="dcard__description">for Nix based systems</p>
+</a>
+</div>
+
 <div class="dcard">
 <a href="https://conan.io/center/crowcpp-crow">
     <img class="dcard__image" src="assets/pkg_logos/conan.png">