docs(model-selection): rename path to match ref

subjects/ai/model-selection/README.md

@@ -1,4 +1,4 @@
-# Model selection methodology
+# Model selection
 
 If you finished yesterday's exercises you should be able to train several Machine Learning algorithms and to choose one returned by GridSearchCV.
 GridSearchCV returns the model that gives the best score on the test set. Yesterday, as I told you, I changed the **cv** parameter to compute the GridSearch with a train set and a test set.