updated gh-pages to be created using the OpenPTV example of two directories

The source files are in the master branch of ``openpiv-python/openpiv/docs`` - using Sphinx. 
Makefile build directory is not ``../../../docs``

the directory /docs/html is the output directory of the Sphinx:

``make html``

and then just 
cd ../../../docs
git add .
git commit -m "new files"
git push origin gh-pages