[Csnd-dev] Minimum CMake Version (also OS version support)

Hi All,

Seeing the issue with Intl::Intl in recent commits, I wanted to poll to see
what the minimum CMake version should be. I see in Debian 11 the latest is
3.18:

https://pkgs.org/download/cmake

Ubuntu 20.04 has 3.16.3.

I think we should do an audit and figure out what the oldest versions of OS
versions we should support. For example, Ubuntu 18.04 has already expired
for regular support, so I think 20.04 should be the oldest version there
(see https://wiki.ubuntu.com/Releases). We can do the same for other
distros/operating systems and add a table to our README.md.

Steven