The installation docs for Ubuntu need new instructions for Ubuntu 23.10

[ppp7032]

The instructions for installing GHCup dependencies on Ubuntu versions >= 20.10 do not work on Ubuntu 23.10. New installation instructions are needed. The relevant output from attempting the installation of the >= 20.10 dependencies on 23.10 is shown below:

Note, selecting 'libffi8' instead of 'libffi8ubuntu1'
E: Unable to locate package libncurses5
E: Unable to locate package libtinfo5

[hasufell]

Well, you need ncurses5 for older GHCs. This is a f*ckup of debian:

• https://answers.launchpad.net/ubuntu/+source/ncurses/+question/707838
• https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1025964

They don't seem to care about binary compatibility.