added small intro to Readers documentation

contrib/Python/doc/readers.rst

@@ -1,11 +1,9 @@
 Readers
 ===============
 
-Intro
-----------
-
-Examples
-----------
+Data readers are used by the computational network to provide information about the data, 
+to load minibatches of data into memory, and to attach this memory to the input nodes in 
+the network. The CNTK Python API currently supports the following reader classes.
 
 Usage
 -------