Add debugging/testing public reachability guide with Kubo

## What

Add a new debugging guide for public reachability based on the new command introduced. by https://github.com/ipfs/kubo/pull/11184

## Why

Public reachability is the bread and butter for IPFS nodes and necessary for the following things to work:

- **Direct data fetching**: Other nodes can fetch data directly from your node without NAT hole punching.
- **Browser access**: Web browsers can connect to your node directly for content retrieval.
- **DHT participation**: Your node can act as a DHT server, helping to maintain the distributed hash table and making content routing more robust.

Up until now, we didn't have any way to debug public reachability. https://github.com/ipfs/kubo/pull/11184 introduces a new command to Kubo which should help with this.

- cc https://github.com/ipfs/kubo/issues/6952