Add images to gitignore and fix latex formula

Two minor changes:
 - Add eps and png images to the gitignore file
 - Fix a typo in the plotting function f(x)

.gitignore

 *.py
 *.swp
 *.swo
+*.png
+*.eps

README.md

@@ -128,7 +128,7 @@ the cropped parabola f(x), which is limited y=4 for x>=2.
     f(x) = \left\{\begin{array}{lr}
               x^2, & \text{for } x < 2\\
               4, & \text{for } 2 \leq x
-            \end{array}\right\.
+            \end{array}\right.
 ```
 
 The final plot should look like this.