modify docstring for upsampling of DeepLabV3Plus

Author: munehiro-k

segmentation_models_pytorch/decoders/deeplabv3/model.py

@@ -129,7 +129,8 @@ class DeepLabV3Plus(SegmentationModel):
             Available options are **"sigmoid"**, **"softmax"**, **"logsoftmax"**, **"tanh"**, **"identity"**,
                 **callable** and **None**.
             Default is **None**
-        upsampling: Final upsampling factor. Default is 4 to preserve input-output spatial shape identity
+        upsampling: Final upsampling factor. Default is 4 to preserve input-output spatial shape identity. In case
+            **encoder_depth** and **encoder_output_stride** are 3 and 16 resp., set **upsampling** to 2 to preserve.
         aux_params: Dictionary with parameters of the auxiliary output (classification head). Auxiliary output is build
             on top of encoder if **aux_params** is not **None** (default). Supported params:
                 - classes (int): A number of classes