added introduction and installed versions section

related to #68

docs.it4i/software/nvidia-cuda.md

 # NVIDIA CUDA
 
-Guide to NVIDIA CUDA Programming and GPU Usage.
+## Introdcution
+
+CUDA® is a parallel computing platform and programming model developed by NVIDIA for general computing on graphical processing units (GPUs).
+
+## Installed Versions
+
+For the current list of installed versions, use:
+
+```console
+$ ml av CUDA
+```
 
 ## CUDA Programming
 
 The default programming model for GPU accelerators is NVIDIA CUDA. To set up the environment for CUDA, use:
 
 ```console
-$ ml av cuda
-$ ml cuda **or** ml CUDA
+$ ml CUDA
 ```
 
 If the user code is hybrid and uses both CUDA and MPI, the MPI environment has to be set up as well. One way to do this is to use the `PrgEnv-gnu` module, which sets up the correct combination of the GNU compiler and MPI library: