1. Removed the duplicate paragraph "To download images with Bing Image
Search..." under the `Gathering Data` > `cleon` section.
2. Added hyperlinks to https://book.fast.ai for the phrase
"book's website". Specifically, in the `Gathering Data` and `State of
deep learning` sections.
3. Corrected the hyperlink to https://book.fast.ai for the phrase
"book's website" in the `Deploying your app` section.
