Update documentation for prepending EE modules

The documentation for prepending EE modules needs to be updated to contain the following:

1. prepend should be the last line of the file
2. If a module or class defines validators that depend on class methods or constants, those class methods or constants should be defined outside of the module or class. This allows EE to redefine them before they are used. This is only necessary if the intention is to redefine them in EE