Document how to get encrypted connections to clusters.

On linux and Mac, when you install (`pip3 install couchbase`), we build the bindings as well.  If you have openssl (or libssl-dev, etc...) installed, good for you.  You can make a couchbases://<some ip or hostname> connection just fine.  But if not, you get a LCB_ERR_SDK_FEATURE_UNAVAILABLE error upon connection.

So – we don't seem to document what to do.  Seems like in the doc discussing ssl/tls, we could start with this?  IDK about windows (and don't want to), but I'd imagine there is something we need to do there as well?