docs: update link to `perf` wiki

docs: update link to perf wiki

https://perf.wiki.kernel.org/ is now a permanent http redirect to https://perfwiki.github.io/, which itself is an html redirect to https://perfwiki.github.io/main/, but let's just link to the root and let the second redirection be a detail on their side.

Since the second redirection is not an http redirection, it won't light up the linkcheck, so we don't have to add an equivalent line to what was previously there.