add python-nix-template to the omnix registry

[cameronraysmith]

see

• feat(registry): adds reference to python-nix-template juspay/omnix#424

this should eventually allow

python-nix-template/README.md

Lines 13 to 16 in 7d17d0d

	```sh
	nix --accept-flake-config run github:juspay/omnix -- \
	init github:sciexp/python-nix-template -o new-python-project
	```

to be simplified to om cli installation and something like

om init python-nix-template -o new-python-project