Doc: Simplify Copyright line in README (GH-10287)

This also makes it consistent with other places like:

- https://docs.python.org/dev/copyright.html
- https://www.python.org/ footer
- https://github.com/python/cpython/blob/e42b705188271da108de42b55d9344642170aa2b/Python/getcopyright.c#L7