Updated db documentation.

chipathlon/db.py

@@ -303,7 +303,14 @@ class MongoDB(object):
 
         Validates and gets samples for the given experiment.  Experiments must
         have control and signal samples of the provided file_type to be
-        considered valid.
+        considered valid.  Returns a tuple with three values (valid, msg, data)
+        valid -- Whether or not the accession / file_type combo is a valid exp
+        msg -- Why it is or is not valid
+        data -- A dictionary containing a list of all control / sample documents.
+        
+        The data dictionary has two keys, "control" and "signal", each one containing
+        a list of all metadata related to the experiment samples.  The sample metadata
+        is taken directly from Mongo.
         """
         valid = True
         msg = ""