add 'native' documention to website

Needed SSL support for PG.

This line in the connection manager appears to be undocumented
```
this.pg             = this.config.native ? require(pgModule).native : require(pgModule)
```

Which is suggested to allow ssl support by this thread:
https://github.com/brianc/node-postgres/issues/25

And appears to work.

So here is documentation for the next person.