update: better intro

[salmad3]

Context

• Changes the approach of the introduction to offer a better overview.
• Presents general themes with mention of core components that link to the respective overview document.

TO DO

• Include an architecture/framework diagram to showcase "all of libp2p". (Will be requested to Crcle and doesn't need to hold up pushing these changes).

Latest preview

Please view the latest Fleek preview here.

[salmad3]

Thank you for your review, @p-shahi.

Based on your feedback, I have updated the "Why libp2p?" section to improve the expression of the features and benefits. I have also used this PR to update all occurrences of "portal" to "site" throughout the site and added the "Related Projects" section back, as suggested.

I also changed the "About libp2p" section to "Background" and have modified the content to focus on the "P2P shortcomings" that libp2p aims to address, as this fits better into the document flow and leads into the "Why libp2p?" section about libp2p's features and capabilities. I am still in favor of including a sub-section about "libp2p and the internet" that discusses the conceptual models behind libp2p and its potential role in shaping the future of the web. However, if there are strong objections to this, we can leave it out as it is more complementary to the document.