docs: Rewrite README (& add echo.rs example)

[matheus23]

Description

• Rewrote the README
• Renamed iroh-router/examples/custom-protocol.rs to search.rs (It's not a "custom" protocol. Just a protocol.) Removed "custom" wording
• Added a simpler echo.rs example (used in the README)

Notes & open questions

• In the "repository structure" section, I describe the purpose of some crates, but not all. Since stuff will be moving around in the coming weeks, I think that's, fine, but someone please tell me if we should do sth differently there.

Change checklist

• Self-review.
• Documentation updates following the style guide, if relevant.
• Tests if relevant.
• All breaking changes documented.

[github-actions]

Documentation for this PR has been generated and is available at: https://n0-computer.github.io/iroh/pr/2960/docs/iroh/

Last updated: 2024-11-26T11:52:34Z

[github-actions]

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Last updated for commit: 7dc49c5

[flub]

Great improvements!