README.md: Add Karabiner Elements link

[perlun]

Seil doesn't work since quite a long time ago (Sierra, High Sierra and now Mojave), so it makes sense to update the links.

[susam]

Thanks for the pull request. However, I am afraid I am not going to merge this. The documentation is already pretty clear that Seil was applicable for OS X, i.e., until OS X 10.11 El Capitan.

For macOS 10.12 Sierra and later versions, the documentation suggests using a builtin feature of macOS available at Apple menu > System Preferences > Keyboard > Modifier Keys. Therefore I do not see the need for the change in this pull request.

[perlun]

Hi @susam

Thanks for the pull request. However, I am afraid I am not going to merge this. The documentation is already pretty clear that Seil was applicable for OS X, i.e., until OS X 10.11 El Capitan.

Sure, do whatever you like. I just personally think it's a bad idea to link people to a dead project. The Seil project web page states that on its front page that:

This application is for older macOS.
Please use Karabiner-Elements since macOS Sierra.

If you don't like the way my PR was phrased, feel free to improve on it, e.g. state that "For older macOS versions, use Seil". The way it's phrased right now doesn't make it overly clear that this part of the README.md applies only to those versions.