You can clone with
HTTPS or Subversion.
For XCode 4 it is best to use the command line right now.
For a break down for the command line parameters you can check out a Stack Overflow answer.
The basic command you need is:
$ mogenerator --model ~/code/iphoneApp/IphoneApp.xcdatamodeld/IphoneApp6.xcdatamodel
Please take note that the model is pointed to the current version of the model.