Add warning that self signed SSL certs are not supported.

[zachvanduyn]

We should probably stuff it in the compliance config, and add it to to the Stellar.org/developers docs.

[jedmccaleb]

Why aren't they supported?

[bartekn]

This is not secure. Golang will simply error when trying to connect to such server. More info: https://security.stackexchange.com/a/8112

[zachvanduyn]

There's not a descriptive error on this one, at least to the end user.

Took me a little bit to find this out when customers were trying to setup compliance with self-signed certs.

[bartekn]

OK, will make the error message better (if possible).