Show sponsors in the README or on the website.

This is part of the requirements to be able to use the platforms that could be used in the performance group (see https://github.com/expressjs/perf-wg/issues/5#issuecomment-2830661578). I'm opening this issue to track it, since a decision needs to be made about where this should be displayed (@wesleytodd likely has more context on the terms).

I suppose @expressjs/docs-wg should be involved here as well, since this involves the website.