lang/php8[01]: Update UPDATING

There are some cases at least when using ports/portmaster php8[01]
reinstalltion do not properly overwrite php.conf file omitting openssl
as a default module. Additionally if we are using pkg then
php8[01]-openssl needs to be manually removed otherwise both the old
module and builtin module tried to be loaded while restarting php-fpm
service.

This note defines these cases in UPDATING.

Reported by: dim
Sponsored by: Bounce Experts