RF: update check_integrity docstring

Author: Katelyn Begany

brainx/modularity.py

@@ -663,12 +663,14 @@ def store_best(self):
         self.bestindex = copy.deepcopy(self.index)
 
     def check_integrity(self, partition):
-        """ Raises error if partition structure is invalid """
+        """ Raises error if partition structure contains
+        empty partitions or Nan values"""
 
         # Raise error if any partition is empty
         if [partition[key] == set([]) for key in partition.keys()]:
             raise ValueError("Partition index %s is empty" % (key))
 
+        # Raise error if any partition contains NaN value(s)
         if [np.isnan(value) for sets in partition.values() for value in sets]:
             raise ValueError("Partition contains NaN(s)")