core module doc updated
+################################################################################
+# Copyright (c) 2021. ContinualAI. All rights reserved. #
+# Copyrights licensed under the MIT License. #
+# See the accompanying LICENSE file for terms. #
+# #
+# Date: 5-5-2021 #
+# Author: Antonio Carta, Vincenzo Lomonaco #
+# E-mail: contact@continualai.org #
+# Website: continualai.org #
+################################################################################
+
+"""
+The core module offers fundamental utilities (classes and data structures) that
+can be used by inner Avalanche modules. As for now, it contains only the
+Strategy Callbacks definition that can be used by the :py:mod:`training`
+module for defining new continual learning strategies and by the
+:py:mod:`evaluation` module for defining new evaluation plugin metrics.
+"""
+
from abc import ABC
from typing import Generic, TypeVar
