Document the change in the previous commit about loading the config file

When libssl is initialised it will attempt to load any config file. This
ensures any system_default configuration (as per
https://github.com/openssl/openssl/pull/4848

) is used.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5818)