Add Cross-Platform/Distribution Compatibility about apt-select

[jblakeman]

Without having the Ubuntu release name set, pulling correct information about mirrors from Launchpad would either need a default release name or have a target release command line option. Since alternative mirrors are usually inconsistent at the frequency at which they update each release, using a default release name could lead to misleading status reports.

Alternatively, non-Ubuntu distributions could default to latency only reporting.

A better solution might be to use latency only reporting for non-Ubuntu systems unless a valid Ubuntu release name is specified as a command line argument.

[luckydonald]

Could the platform be set as flag?
I.e. run on the server uname -v
And use

apt-select --kernel="#1 SMP Debian 3.16.43-2+deb8u5 (2017-09-19)"

Is there some way to run it outside of linux, to just get a list of mirrors?
Basically a --ignore-not-linux?
Trying to run it on a mac next to the server. Can't install python on the server.