Fixed broken comment on start def

IPython/nbconvert/nbconvertapp.py

@@ -136,7 +136,7 b' class NbConvertApp(BaseIPythonApplication):'
 
     def start(self, argv=None):
         """
-        Entrypoint of NbConvert application.
+        Ran after initiialization completed
         """
         super(NbConvertApp, self).start()
         self.convert_notebooks()