Another little change

readme.md

@@ -4,5 +4,5 @@ It was done in three steps:
 1. Parsing of the wikipedia dump (an XML file) using the etree library
 2. Manipulation of the csv files to create the inverted index and other files needed for the next step
 3. Creating the graphs
-<h2> How to run </h2>
+<h3> How to run </h3>
 The project is written in Python using Jupyter Notebook. In the first cell you'll find the libraries that are needed to run the project. You can install them using pip.