Update trouble shooting (#3994)

docs/trouble_shooting.md

@@ -1,6 +1,6 @@
 ## Trouble Shooting
 
-We list some common troubles faced by many users and their corresponding solutions here. Feel free to enrich the list if you find any frequent issues and have ways to help others to solve them.
+We list some common troubles faced by many users and their corresponding solutions here. Feel free to enrich the list if you find any frequent issues and have ways to help others to solve them. If the contents here do not cover your issue, please create an issue using the provided templates and make sure you fill in all required information in the template.
 
 - Compatibility issue between MMCV and MMDetection; "ConvWS is already registered in conv layer"; "AssertionError: MMCV==xxx is used but incompatible. Please install mmcv>=xxx, <=xxx."
 
@@ -22,3 +22,9 @@ We list some common troubles faced by many users and their corresponding solutio
     1. If those symbols are CUDA/C++ symbols (e.g., libcudart.so or GLIBCXX), check     whether the CUDA/GCC runtimes are the same as those used for compiling mmcv.
     2. If those symbols are Pytorch symbols (e.g., symbols containing caffe, aten, and  TH), check whether the Pytorch version is the same as that used for compiling mmcv.
     3. Run `python mmdet/utils/collect_env.py` to check whether PyTorch, torchvision,   and MMCV are built by and running on the same environment.
+
+- setuptools.sandbox.UnpickleableException: DistutilsSetupError("each element of 'ext_modules' option must be an Extension instance or 2-tuple")
+
+    1. If you are using miniconda rather than anaconda, check whether Cython is installed as indicated in [#3379](https://github.com/open-mmlab/mmdetection/issues/3379).
+    You need to manually install Cython first and then run command `pip install -r requirements.txt`.
+    2. You may also need to check the compatibility between the `setuptools`, `Cython`, and `Pytorch` in your environment.