Add simple_bind example

[JedimEmO]

It might be prudent to add a full example on how you would use simple bind to do authentication & membership lookup for authorization. I'll make the example work with the proposed test docker in #5

[JedimEmO]

Added a small example for authenticating with simple_bind, start_tls: https://github.com/coder543/rust-cldap/pull/8/files