docs: add deep dive into kademlia

[danielrachi1]

What was wrong?

The existing article about Kademlia in the book was a bit shallow.

How was it fixed?

I wrote an article based on my understanding of the protocol. I believe it would complement the current information in the book.

(I wrote this several weeks ago as I was getting started with the portal network, but I realized that this might be a good thing to have in the docs.)

To-Do

• Add entry to the release notes (may forgo for trivial changes)
• Clean up commit history
• Have someone check that the info in the document is accurate, and relevant to Trin.

[njgheorghita]

Thanks for the write-up! These kinds of explanations are very useful, especially to newcomers. However, this content feels more appropriately located inside of www.ethportal.net. It's general information that's relevant to all clients, and I'd like to start slimming down our docs to only containing trin-centric information. I'd recommend opening up a pr with this information (along with what existed in this page before your pr) over in https://github.com/ethereum/portal-website.

[danielrachi1]

I agree, we should keep the book for trin-exclusive info and this is better placed at the general portal network docs.

Just opened ethereum/portal-website#7