[Docs] the link should direct to the mdBook website

[shubhangi013]

Is your feature request related to a problem? Please describe.
The link in Getting started that tells us about Browse the LibAFL book (WIP!) with (requires [mdbook](https://github.com/rust-lang/mdBook)) , has link to mdBooks repository

Describe the solution you'd like
It should redirect to https://rust-lang.github.io/mdBook/index.html

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[shubhangi013]

I can work on this easily.

[soumya-78]

Can you please explain what you are trying to solve through this issue @shubhangi013 ?
Like what i encounter after installing mdbook through cargo install mdbook if we run the command cd docs && mdbook serve then the mdBook documentation will open in localhost port.

[domenukk]

I don't have a strong preference if we link to their book or github. Worst case ppl can google :) But feel free to open a PR if you prefer to update the link of course