Minor cleanup of categorical example

Author: timhoffm

examples/lines_bars_and_markers/categorical_variables.py

@@ -3,11 +3,8 @@
 Plotting categorical variables
 ==============================
 
-How to use categorical variables in Matplotlib.
-
-Many times you want to create a plot that uses categorical variables
-in Matplotlib. Matplotlib allows you to pass categorical variables directly to
-many plotting functions, which we demonstrate below.
+You can pass categorical values (i.e. strings) directly as x- or y-values to
+many plotting functions:
 """
 import matplotlib.pyplot as plt