adds install troubleshoot for mmcv cuda

Author: lgvaz

docs/INSTALL.md

@@ -79,15 +79,15 @@ We need to provide the appropriate version of the `mmcv-full` package as well as
 #### CUDA-Version Installation Example
 <div class="termy">
 ```console
-$ pip install mmcv-full=="1.3.1" -f https://download.openmmlab.com/mmcv/dist/CUDA_VERSION/TORCH_VERSION/index.html --upgrade
+$ pip install mmcv-full=="1.3.3" -f https://download.openmmlab.com/mmcv/dist/CUDA_VERSION/TORCH_VERSION/index.html --upgrade
 $ pip install mmdet
 ```
 </div>
 
 #### CPU-Version Installation
 <div class="termy">
 ```console
-$ pip install mmcv-full=="1.2.5+torch.1.7.0+cpu" -f https://download.openmmlab.com/mmcv/dist/index.html --upgrade
+$ pip install mmcv-full=="1.3.3+torch.1.8.0+cpu" -f https://download.openmmlab.com/mmcv/dist/index.html --upgrade
 $ pip install mmdet
 ```
 </div>
@@ -97,4 +97,25 @@ $ pip install mmdet
 ```console
 $ pip install yolov5-icevision --upgrade
 ```
-</div>
+</div>
+
+## Troubleshooting
+
+### MMCV is not installing with cuda support
+If you are installing MMCV from the wheel like described above and still are having problems with CUDA you will probably have to compile it locally. Do that by running:
+```
+pip install mmcv-full
+```
+
+If you encounter the following error it means you will have to install CUDA manually (the one that comes with conda installation will not do).
+```
+OSError: CUDA_HOME environment variable is not set. Please set it to your CUDA install root.
+```
+Try installing it with:
+```
+sudo apt install nvidia-cuda-toolkit
+```
+Check the installation by running:
+```
+nvcc --version
+```