docs: add in-depth distributed actors information to kameo book

[tqwewe]

As peer feedback, in-depth information on distributed actors in kameo was lacking. This PR adds sections to the kameo book covering how to use distributed actors, and how it works internally.

Sections added:

• Distributed Actors Overview
• Bootstrapping Actor Swarm
• Dialing and Connecting to Other Nodes
• Registering and Looking up Actors
• Messaging Remote Actors

Closes #50