add sha256 for python.org release data

[JacobCoffee]

Adds sha256 data for a release.

One half of a PR, requiring the other to merge first.
re: python/pythondotorg#1227 (comment)

Other half: python/pythondotorg#2830

[AA-Turner]

Suggested change

	return hashlib.sha256(
	open(filename, "rb").read(),
	).hexdigest()
	return hashlib.sha256(open(filename, "rb").read()).hexdigest()

or

Suggested change

	return hashlib.sha256(
	open(filename, "rb").read(),
	).hexdigest()
	with open(filename, "rb") as f:
	return hashlib.sha256(f.read()).hexdigest()

[hugovk]

[Marking as draft until python/pythondotorg#2830 is merged]