About an Int and separate 1 section in 2

This commits

* a fix because now you need to use an Int instead of a String.
* Separate the section http://cookbook.liftweb.net/#ConnectingToMongo in 2 (one for connect to one and the other in how to use 2 or more).

By the way, there is no `contributors.md` as wrote in http://cookbook.liftweb.net/#LiftCodeContributions