Added more info about categorical_crossentropy
`categorical_crossentropy`  is another term for multiclass log loss. Which seems to be necessary information about `categorical_crossentropy` as `sklearn` has it as `log_loss` hence its beneficial for people migrating from `sklearn` and other people who learned it as `log_loss`.
@@ -38,3 +38,5 @@ categorical_labels = to_categorical(int_labels, num_classes=None)
When using the `sparse_categorical_crossentropy` loss, your targets should be *integer targets*.
If you have categorical targets, you should use `categorical_crossentropy`.
+
+`categorical_crossentropy` is another term for [multi-class log loss](http://wiki.fast.ai/index.php/Log_Loss).
