Update README.md

Author: CamDavidsonPilon

README.md

@@ -30,7 +30,7 @@ Contents
 Interactive notebooks + examples can be downloaded by cloning! )
 
 
-* ['**Prologue.**'](http://nbviewer.ipython.org/urls/raw.github.com/CamDavidsonPilon/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers/master/Prologue/Prologue.ipynb) Why we do it.
+* ['Prologue:'](http://nbviewer.ipython.org/urls/raw.github.com/CamDavidsonPilon/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers/master/Prologue/Prologue.ipynb) Why we do it.
 
 * ['**Chapter 1: Introduction to Bayesian Methods**'](http://nbviewer.ipython.org/urls/raw.github.com/CamDavidsonPilon/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers/master/Chapter1_Introduction/Chapter1_Introduction.ipynb)
     Introduction to the philosophy and practice of Bayesian methods and answering the question "What is probabilistic programming?" Examples include: