bpo-34009: Expand on platform support changes (GH-8022)

Many users won't realise the implications the OpenSSL 1.0.2
minimum version requirement has when it comes to Ubuntu
14.04 and Debian 8, so expand on that in the platform support
section.

Also explicitly note the non-ASCII-based locale requirement for
full Unicode text handling support on non-Windows systems.
1 file changed