(SERVER-136) Add docs for http client SSL config

This isn't a comprehensive list.  The full list may depend upon what is available in your JDK.  We could suggest that users consult JDK documentation -- e.g., the "Protocols" and "Cipher Suites" sections in http://docs.oracle.com/javase/7/docs/technotes/guides/security/SunProviders.html#SunJSSEProvider if the user were using JDK 7 from Oracle.