Add a step by step basic usage guide

[kill9zombie]

Hopefully this should resolve #150

Adds a basic 'direct use' guide for people not so familiar with front end web development.

However, there is a caveat. At the moment examples downloaded from https://h5p.org/content-types-and-applications
don't seem to have the libraries inside the .h5p file!

The H5P docs don't seem to have changed either, so it looks like the libraries should still be there:
https://h5p.org/documentation/developers/h5p-specification

So as it stands, the guide won't work as is with the h5p.org examples. I think we have three options at the moment:

1. Wait until H5P Group fix their examples
2. Wait until H5P Group update their docs (maybe they're moving towards a central download of all content types?)
3. Add a note in the guide to explain what's going on at the moment

Feel free to edit it. Thank you so much for writing this H5P player!