add reference link (#4445)

ppdet/modeling/assigners/simota_assigner.py

@@ -11,6 +11,10 @@
 # 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.
+"""
+This code is refer from:
+https://github.com/open-mmlab/mmdetection/blob/master/mmdet/core/bbox/assigners/sim_ota_assigner.py
+"""
 
 import paddle
 import numpy as np

ppdet/modeling/necks/csp_pan.py

@@ -11,6 +11,10 @@
 # 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.
+"""
+This code is refer from:
+https://github.com/open-mmlab/mmdetection/blob/master/mmdet/models/necks/yolox_pafpn.py
+"""
 
 import paddle
 import paddle.nn as nn