xkcdpass: make available as application

but keep it as a lib, too, because it
can be imported as a module:
https://github.com/redacted/XKCD-password-generator/tree/xkcdpass-1.17.3#using-xkcdpass-as-an-imported-module

pkgs/top-level/all-packages.nix

@@ -3116,6 +3116,8 @@ in
 
   wob = callPackage ../tools/misc/wob { };
 
+  xkcdpass = with pythonPackages; toPythonApplication xkcdpass;
+
   xob = callPackage ../tools/X11/xob { };
 
   z-lua = callPackage ../tools/misc/z-lua { };