Easy install emulators with libretro ppa for Ubuntu

[atilacamurca]

Add installation option to add the libretro ppa for easy installation of emulators.

References

• https://launchpad.net/~libretro/+archive/ubuntu/stable/
• https://www.linuxbuzz.com.br/2016/07/parallel-novo-emulador-de-nintendo-64-do-retroarch--que-faz-uso-da-api-vulkan.html