Expand SSL_CTX_set_default_verify_paths() documentation
Expand SSL_CTX_set_default_verify_paths() documentation

Add some information about the location of the default directory and the
default file.

RT#1051

Reviewed-by: Andy Polyakov <015edf36635e030d5e009e08808a59984e629740@openssl.org>

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl