add copyright & reference

ppcls/arch/backbone/base/dbb_block.py

+# copyright (c) 2023 PaddlePaddle Authors. All Rights Reserve.
+#
+# 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.
+
+# reference: https://arxiv.org/abs/2103.13425, https://github.com/DingXiaoH/DiverseBranchBlock
+
 import paddle
 import paddle.nn as nn
 import paddle.nn.functional as F

ppcls/data/preprocess/ops/operators.py

@@ -872,7 +872,10 @@ class RandomGrayscale(object):
 
 
 class PCALighting(object):
-    """Lighting noise(AlexNet - style PCA - based noise)"""
+    """
+    Lighting noise(AlexNet - style PCA - based noise)
+    reference: https://github.com/DingXiaoH/DiverseBranchBlock
+    """
 
     def __init__(self):
         self.alphastd = 0.1