Added the Demo in ReadMe

[Gilbishkosma]

I have added the demo link in the ReadMe file and also updated the example/index.html file
I have used jsdelivr in order to access the hover-review.minified.js file instead of directly accesing the raw github file.
Cause in 2013, GitHub started using X-Content-Type-Options: nosniff, which instructs more modern browsers to enforce strict MIME type checking. It then returns the raw files in a MIME type returned by the server, preventing the browser from using the file as-intended (if the browser honors the setting).

You can read more about this here

[AviKKi]

@Gilbishkosma add this link in the readme instead, it looks much better, the example in example directory can serve as an simpler example.

[Gilbishkosma]

sure @AviKKi