Create getting started guide for cpp-libp2p

[salmad3]

Done Criteria

TO-DO

Why Important

• Showcases how users can get started with cpp-libp2p.
• Follows the other getting started tutorials on the docs.

[p-shahi]

Ideally this is something the cpp-libp2p maintainers can take on and not the PL libp2p or docs team