Add Unite to Gnome extensions

[glow12121]

There's no Discussions section on this git, so I'll have to publish it here.

Hardpixel has declared Unite won't be published among Gnome extensions anymore. I am sure he had his motives to do so, but if possible I urge to reconsider this. It would be so much more convenient to have Unite back there.

[42Willow]

If this extension really is to be removed from gnome extensions, the readme should be updated.
But I agree installing from gnome extensions is much easier and faster for the user.

As uploading it manually to gnome extensions sounds tedious, there's a way to automate it with GitHub actions.

Resources:

• https://github.com/swsnr/ego-upload

Here is the PR: #355