Update default params for TPOT example

Author: rhiever

README.md

@@ -61,7 +61,7 @@ digits = load_digits()
 X_train, X_test, y_train, y_test = train_test_split(digits.data, digits.target,
                                                     train_size=0.75, test_size=0.25)
 
-tpot = TPOT(generations=5)
+tpot = TPOT(generations=5, population_size=20, verbosity=2)
 tpot.fit(X_train, y_train)
 print(tpot.score(X_test, y_test))
 tpot.export('tpot_mnist_pipeline.py')