To have this template in the Editor you need to put it in the Templates folder when you prepare release package.
If you make release package by hand, then you are manually copying all required templates there, obviously.
Earlier, when Nick Sonneveld was around, we had automatic building script that took all templates from the ags-templates repository, and copied them into release package. So, having them updated in that repository was important. Now, when auto-building is not working, that's rather an option, but still useful, because you may just blindly copy all the files from there when preparing a release.
To put the new template there you need either someone who has commit rights, or make a pull request.
PS. The template's repository does not have any license, only list of contributors. Maybe this is just a formality, but is there supposed to be one?
I'd rather have a confirmation from the template author(s) that the template is complete and may be used in release.
Also, this reminds me that if the template is replaced, we also will have to replace credits in the manual.