refact: identical section headings

README.md

@@ -181,7 +181,7 @@ end
 
 ![figure_2.png](how_to_start_images/figure_2.png)
 
-## (2) Accessing position data
+## Part 2) Accessing position data
 ### 2-1) Loading position data (solitary)
 
 In this instance, we will go through the behavioral data extracted from a sample video. For this specific example, we use one example solitary threat session (mouse #2, session #3) to depict the trajectory of the mouse's movement in space.