Add recommendations for setup resources

[jahvi]

Added a new section for setup resources, the 3rd one is kind of opinionated but I found that it's super useful. I can take it out if it's not too relevant.

[gamort]

Personally I prefer using calls to methods in the Varien_Db_Adapter_Interface for making changes.

Example: a call to addColumn for a column which was already created will not break - Magento automatically checks for existence first and returns successfully if it is found.