message: Update README.md
  Simplified git clone commands
diff: @@ -15,9 +15,7 @@ Getting Visionaray
  The Visionaray git repository can be cloned using the following commands:
  ```Shell
  -git clone https://github.com/szellmann/visionaray.git
  -cd visionaray
  -git submodule update --init --recursive
  +git clone --recursive https://github.com/szellmann/visionaray.git
  ```
  Build requirements
  