[wiki] Add OpenCore to EFI/UEFI Boot Loaders page

[Mike Beaton]

Would there be any interest in my volunteering to add a column for OpenCore
https://github.com/acidanthera/OpenCorePkg to the
https://wiki.ubuntu.com/EFIBootLoaders page?

In case it needs any introduction, OpenCore is a secure, capable UEFI
bootloader under very active development. Some of the development on it has
even fed back into EDK-II. It has featured native Linux auto-detection and
booting (i.e. not chainloading via the GRUB/other distro-native bootloader)
for a short while now, since version 0.7.3
https://github.com/acidanthera/OpenCorePkg/blob/master/Changelog.md.

I worked on the Linux support in OpenCore, and so would be happy to
volunteer to add this info to the wiki page, if it would be considered
relevant enough (I believe it is!) and welcome.

Mike