[Proposal] Add a getting started notebook

[cordasfilip]

Hi I have been playing around with PdfPig, it's an excellent library
Since I have been playing around with it, I created a small notebook to view the results that some else that starting might find useful. https://gist.github.com/cordasfilip/c6d2510b358323dc2f71c843460cbcdf

here is the document I used to test it (it's some Microsoft demo pdf) you can use any document in it you want Benefit_Options.pdf

I think it's a ok place to start because it has document preview. I could also make a code space for this on github so people can test it really quickly. If you have any questions, please ask.