Added autonat example readme

Author: petarjuki7

examples/autonat/README.md

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+# AutoNAT Client Example
+
+This example demonstrates NAT detection and connectivity strategies using libp2p's AutoNAT protocol.
+
+## How It Works
+
+The application:
+1. Detects whether your node is behind NAT/firewall (private) or publicly accessible
+2. Establishes appropriate connectivity based on NAT status
+3. Registers with a rendezvous point for peer discovery
+
+### Private Node Behavior
+When behind NAT (most home networks):
+- Detects private NAT status through AutoNAT probes
+- Creates a relay reservation with a public relay node
+- Uses the relay address to register with a rendezvous point
+- Other peers can connect through the relay circuit
+
+### Public Node Behavior
+When publicly accessible:
+- Confirms public status with high confidence (2+ successful probes)
+- Registers direct address with rendezvous point
+- Other peers can connect directly without relay
+
+## Running the Example
+
+```
+cargo run
+```
+
+For custom options:
+```
+cargo run -- --listen-port 4001
+```
+
+## Troubleshooting
+
+- If you can't register with the rendezvous point, check that you have a valid relay connection
+- Connection timeouts may indicate firewall issues blocking libp2p protocols