Images of NLTK articles (#468)

* images for webscraping blog

Images that are use in Web Scraping blog.

* Banner Image for WebScraping

This is the banner image that you asked for to use on the blog. So here, I changed it for Web Scraping Introduction Blog.

* image for chatbot content

* flowchart image to build a chatbot with NLTK

* Images of ChatBot with NLTK article

Author: vaishali-sharma-20