Add docstring for rcs, vcs modules

This patch adds docstring to explain what rcs/vcs modules are clearly.

Change-Id: Ie0904115f4feb47fb6e0da814204fd28326e316e

stackalytics/processor/rcs.py

@@ -34,6 +34,8 @@ class RcsException(Exception):
 
 
 class Rcs(object):
+    """Base object for Review Control System"""
+
     def __init__(self):
         pass
 

stackalytics/processor/vcs.py

@@ -28,6 +28,8 @@ LOG = logging.getLogger(__name__)
 
 
 class Vcs(object):
+    """Base object for Version Control System"""
+
     def __init__(self, repo, sources_root):
         self.repo = repo
         self.sources_root = sources_root