Improved issues template

.github/issue_template.md

@@ -17,6 +17,7 @@ Keep only your type and delete the rest. You might select multiple topics:
 - Other (type your own type)
 
 ### Your system configuration
+**OpenCV version** (installed with `apt-get install libopencv-dev` or OpenCV 2.X or OpenCV 3.X):
 **Operating system** (`lsb_release -a` on Ubuntu):
 **CUDA version** (`cat /usr/local/cuda/version.txt` in most cases):
 **cuDNN version**: