fix docker run command in README.md

add docker gpu command support, 
remove a useless whitespace in command

README.md

@@ -74,8 +74,12 @@ export PYTORCH_ENABLE_MPS_FALLBACK=1
 Provided docker image is based on NGC PyTorch repository. To quickly try out visualizer in Docker, run the following:  
 
 ```sh
+# before you build the docker container, make sure you have cloned this repo, and downloaded the pretrained model by `python scripts/download_model.py`.
 docker build . -t draggan:latest  
-docker run -p 7860: 7860 -v "$PWD":/workspace/src -it draggan:latest bash  
+docker run -p 7860:7860 -v "$PWD":/workspace/src -it draggan:latest bash
+# (Use GPU)if you want to utilize your Nvidia gpu to accelerate in docker, please add command tag `--gpus all`, like:
+#   docker run --gpus all  -p 7860:7860 -v "$PWD":/workspace/src -it draggan:latest bash
+
 cd src && python visualizer_drag_gradio.py --listen
 ```
 Now you can open a shared link from Gradio (printed in the terminal console).