Add documentation on parsing

[2016rshah]

So I was poking through the Parsing example and it seemed simple enough. But I originally struggled with extracting information from the AST. I wasn't sure how to actually find something, like the name of the author of the LaTeX file.

After thinking about it for a little while, I figured it out! But I thought it might be useful if I added a bit of documentation to give a bit more of an in depth worked example on parsing. Would you be interested in my help documenting that?

If so, where would you like me to add my two cents? On one hand I could just add to the parsing example, comment the code, etc. and then send in a pull request to that repo with the updated example. Or I could add to this guide instead, in which case I might need a bit more help to make sure I contribute correctly and all

Let me know what you think!