Add ignore suggestions to pelicanconf.py setup

[nayyarv]

I was creating my jupyter notebooks directly in the content dir and was getting an error since the pelican processor would see both the checkpoints and the ipynb files which would have identical metdata and be rather confused.

WARNING: There are 2 items with slug "tosser" with lang en:
  | /Users/varun/Documents/github/nayyarv.github.io/content/Tosser.ipynb
  | /Users/varun/Documents/github/nayyarv.github.io/content/.ipynb_checkpoints/Tosser-checkpoint.ipynb
WARNING: There are 2 original (not translated) items with slug "tosser":
  | /Users/varun/Documents/github/nayyarv.github.io/content/Tosser.ipynb
  | /Users/varun/Documents/github/nayyarv.github.io/content/.ipynb_checkpoints/Tosser-checkpoint.ipynb
CRITICAL: RuntimeError: File /Users/varun/Documents/github/nayyarv.github.io/output/tosser.html is to be overwritten
make: *** [html] Error 1

I think it might not be a bad idea to include an ignore section in your doc as well so people like me are sorted from the get go!

[danielfrg]

Thanks for the PRs!

[nayyarv]

Haha nw, this was the fastest a PR of mine has ever been merged! Glad to help, code is super easy to read and understand, so it was no trouble whatsoever and it's useful to boot too!