docs: fix Ubuntu ppa repository name

[miquelbeltran]

Description

Went through the installation and found that there is a typo in the README.

$ sudo add-apt-repository ppa:flexiondotorg/quickgui
ERROR: ppa 'flexiondotorg/quickgui' not found (use --login if private)

But with the quickemu instructions it all work:

$ sudo apt-add-repository ppa:flexiondotorg/quickemu
...
$ sudo apt-get install quickgui
(all good)

Seems that the right ppa is the same as the one for quickemu and one with quickgui in it.

• Related 7 Levels of PPA Hell #196 (ticket seems related, although they mention Asahi, I am on vanilla Ubuntu)

Type of change

• Documentation (updates the documentation)

Checklist:

• I have made corresponding changes to the documentation