install pygraphviz on windows 10

1. Download graphviz-2.38.msi from the graphviz Graphviz site https://graphviz.gitlab.io/_pages/Download/windows/graphviz-2.38.msi
2. Install the msi (I used cmd with Admin priviledges)
   msiexec /a graphviz-2.38.msi
3. For some reason this doesn't add Graphviz to your system path, so you need to do that manually. For me this was
   SET PATH=%PATH%;C:\Program Files (x86)\Graphviz2.38\bin
4. I then had to get a specific Windows pygraphviz wheel from this really useful site, specifically pygraphviz-1.3.1-cp34-none-win_amd64.whl https://www.lfd.uci.edu/~gohlke/pythonlibs/#pygraphviz
5. Once I had this I then installed it using pip/mingw32 to my virtual environment
   $ pip install pygraphviz-1.3.1-cp34-none-win_amd64.whl