Add refrences and furthur reading

[ankit27kh]

Feature details

Currently, very rarely, you can find some links to external sources in the codebook. It will be much better to provide links to outside sources like books, articles and research papers in every node.

Additional information

Important terms can be hyperlinked to external sources. Relevant papers should be referenced in the text, and a reference list should be made at the end of each node.

A dictionary of terms can also be made as a separate node.

[alvaro-at-xanadu]

These are very good suggestions! We'll do our best to provide relevant references throughout the book in the following updates.