add example of likely kwargs to test() docstring

IPython/testing/__init__.py

@@ -17,6 +17,12 b' def test(**kwargs):'
     """Run the entire IPython test suite.
 
     Any of the options for run_iptestall() may be passed as keyword arguments.
+
+    For example:
+    
+        IPython.test(testgroups=['lib', 'config', 'utils'], fast=2)
+    
+    will run those three sections of the test suite, using two processes.
     """
 
     # Do the import internally, so that this function doesn't increase total