Sponsor releaser

Your company logo will be displayed in the project's README, doc, PyPI web page and gmpy.dev (my personal website). In addition you can ask me to publish a new release of psutil. Usually I fix bugs on master, then I wait 4-5 months before creating a new release because it's time-consuming. With this tier, if there's a bug you care about which is already fixed in master, you can ask me to make a new psutil release immediately.