Update masking.py

- header

Author: MMathisLab

cebra/data/masking.py

@@ -1,3 +1,18 @@
+# Please see LICENSE.md for the full license document:
+# https://github.com/AdaptiveMotorControlLab/CEBRA/blob/main/LICENSE.md
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
 import random
 from typing import Dict, Optional