Docs: add Nix and NixOS install instructions

README.md

@@ -109,6 +109,34 @@ package.
 sudo port install ctpv
 ```
 
+### Nix
+
+#### Nix package
+
+```console
+nix-env -ivf cptv
+nix profile install nixpkgs#cptv # with flakes enabled
+```
+
+#### NixOS and HomeManager
+
+If you don't need to call it directly and
+just want to use it through lf:
+
+```nix
+programs.lf = {
+  previewer = {
+    keybinding = "i";
+    source = "${pkgs.ctpv}/bin/ctpv";
+  };
+  extraConfig = ''
+    &${pkgs.ctpv}/bin/ctpv -s $id
+    cmd on-quit %${pkgs.ctpv}/bin/ctpv -e $id
+    set cleaner ${pkgs.ctpv}/bin/ctpvclear
+  '';
+}
+```
+
 ## Integration
 
 ### lf file manager