[ENHANCEMENT] Clarify specifying URL in message about registering new package

[mtfishman]

See the new instructions here: https://github.com/ITensor/ITensorRegistry?tab=readme-ov-file#registering-a-package

Maybe we should just link to those in

ITensorPkgSkeleton.jl/src/ITensorPkgSkeleton.jl

Lines 158 to 181 in 07abef5

	function pkg_registration_message(; pkgname, path)
	return """
	The package "$pkgname" has been generated at "$path".
	To register the package in the [ITensor registry](https://github.com/ITensor/ITensorRegistry), first add
	the registry if you haven't already with:
	```julia
	julia> using Pkg: Pkg
	julia> Pkg.Registry.add(url="https://github.com/ITensor/ITensorRegistry")
	```
	or:
	```julia
	julia> Pkg.Registry.add(url="git@github.com:ITensor/ITensorRegistry.git")
	```
	if you want to use SSH credentials, which can make it so you don't have to enter your Github ursername and password when registering packages.
	Then, use `LocalRegistry.jl` to register the package. First, you should add `LocalRegistry.jl` in your global environment. Then, activate the package and call:
	```julia
	using LocalRegistry: LocalRegistry
	LocalRegistry.register()
	```
	"""
	end

so we don't have to repeat things and can just update them in one place.