README python command update

[Darcwing]

The current command to start the "tiny Web Server" is possibly outdated. You may want to update it to something like:

Python 2

python -m SimpleHTTPServer 8000

Python 3

python -m http.server 8000

Newbs on a MAC, like me can get discouraged with something this simple...

[robinsmidsrod]

Would you like to try and create a pull request for me to merge? Remember that the source files are in the _site/ folder.