Update README.md

Changed the download location to the correct VG release containing the doxygen filter python script and changed the documentation

Author: jdsika

README.md

@@ -88,7 +88,7 @@ Documentation
 
 In order to generate the doxygen documentation for OSI, please follow the following steps: 
 1. Install [Doxygen](http://www.stack.nl/~dimitri/doxygen/download.html), set an environmental variable 'doxygen' with the path to the binary file and add it to PATH `<old-path>;%doxygen%`.
-2. Clone the [git repository containing the filter proto2cpp.py](https://github.com/vgteam/vg.git). The filter can then be found under vg/contrib/proto2cpp.
+2. Download the [vg-1.5.0.zip](https://github.com/vgteam/vg/releases/tag/v1.5.0). Unpack and copy the content of folder \vg-1.5.0\contrib\proto2cpp to your desired `<path-to-proto2cpp.py>`
 3. Install [graphviz-2.38](http://www.graphviz.org/Download_windows.php ), set an environmental variable 'graphviz' with the path to the binary file and add it to PATH `<old-path>;%graphviz%`.
 4. From the cmd navigate to the build directory and run: 
 ```cmd