Add readme to this exercise

README.md

@@ -97,4 +97,14 @@ Additionally, the following class was added to the project:
     view/graphics/PaintableSpline.java
     
 ### Expected behavior:
-Spline interpolation can be painted.
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+Spline interpolation can be painted.
+
+## Exercise 8
+This exercise is based on the eleventh lecture about a more effcient spline interpolation method.
+
+In this exercise we need to implement this new method in the following classes:
+    model/Spline.java
+    view/graphics/PaintableSpline.java
+    
+### Expected behavior:
+Spline interpolation can be painted as before.
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