Please add the mirror for Gentoo Linux


[Gentoo](https://www.gentoo.org/) is a Linux distribution built using the Portage package management system. Unlike a binary software distribution, the source code is compiled locally according to the user's preferences and is often optimized for the specific type of computer. Precompiled binaries are available for some larger packages or those with no available source code.

There is a [number of Gentoo mirrors around the globe](https://www.gentoo.org/downloads/mirrors/), but in China there is only reliable is Tsinghua one. It would be amazing to mirror package trees as well. Setting up the mirror is straightforward, see [Setting up the new mirror](https://wiki.gentoo.org/wiki/Project:Infrastructure/Mirrors/Source) page.

Start with the linked Gentoo mirror list and the Gentoo “Setting up the new mirror” guide, then inspect this repository for the configuration that defines hosted mirrors. Confirm the required Gentoo package trees and hosting details, and consider the work done when a reliable China-based Gentoo mirror is configured and available.

Written by the indexing model from the issue text.