Add registry entry for pyenv

flake.nix

@@ -94,6 +94,16 @@
                       url = "https://git.xenia.me.uk/xenia/nixos.git?ref=main";
                     };
                   };
+                  pyenv = {
+                    from = {
+                      type = "indirect";
+                      id = "pyenv";
+                    };
+                    to = {
+                      type = "git";
+                      url = "https://git.xenia.me.uk/utils/pyenv.git";
+                    };
+                  };
                   jupyter = {
                     from = {
                       type = "indirect";