Document alternative SSH ports for restricted networks

Some developers find themselves on networks that block outbound port 22
and cannot use a VPN. Document that gitolite.kernel.org also listens on
ports 2222 and 443 as alternatives.

The recommendation is to try port 2222 first, and fall back to port 443
if that is also blocked. A note explains that port 443 may not work on
networks with deep packet inspection, and that an obfuscating VPN may
be the only option in that case.

Assisted-by: claude-sonnet-4-6
Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>