Remove Powerpoint, add notebook from table of contents

Author: gjbex

source-code/cython/README.md

@@ -2,7 +2,8 @@
 Examples of how to use Cython and its impact on performance.
 
 ## What is it?
-1. `cython.pptx`: Powerpoint presentation on Cython.
+1. `cython.ipynb`: Jupyter notebook on Cython, illustratiing dynamic
+   memory management.
 1. `HellowWorld`: simplest possible code to illustrate the build process.
 1. `Numpy`: example of how to access numpy arrays from Cython.
 1. `Exceptions`: exception handling in Cython code.