Add Gentoo Linux overlay an ebuilds

[vaxxabait]

[devbisme]

Thanks for the contribution. I'm not familiar enough with Gentoo to understand what benefits this provides. If it is solely for Gentoo users, then I would rather pull it into a separate branch that those users could install from and that they can submit PRs against in order to keep it up to date.

[heeplr]

@vaxxabait that's awesome! But you might want to create the PR over at the gentoo repo. They can add it to portage (but even if not, it can be found there in the list of unmerged PRs).