Update readme

Author: danimhr

README.md

@@ -31,12 +31,23 @@ RUST_LOG=INFO cargo run -- run \
   --server-url https://quorum-1.pyth.network \
   --server-url https://quorum-2.pyth.network \
   --server-url https://quorum-3.pyth.network \
-  --secret-key /path/to/secret.key \
+  --signer-uri file:///path/to/secret.key \
   --wormhole-pid H3fxXJ86ADW2PNuDDmZJg6mzTtPxkYCpNuQUTgmJ7AjU
 ```
 
 You can specify multiple `--server-url` flags to broadcast observations to more than one server.
 
+✅ **Note on `--signer-uri`:**  
+This argument specifies the signer backend and is compatible with the formats supported by the [Wormhole Guardian Signer](https://github.com/wormhole-foundation/wormhole/blob/main/docs/guardian_signer.md).
+
+**Supported schemes:**
+- `file://<path-to-file>` — Load an **armored OpenPGP secp256k1 private key** from a file.
+- `amazonkms://<key-id-or-arn>` — Use a key stored in AWS KMS. The key must support `ECDSA_SHA_256` and use the `ECC_SECG_P256K1` curve.
+
+**Example using AWS KMS:**
+```bash
+--signer-uri amazonkms://arn:aws:kms:us-west-2:123456789012:key/abcde-1234-5678
+```
 
 ---
 
@@ -47,7 +58,7 @@ Instead of CLI flags, you can also set environment variables:
 ```bash
 export PYTHNET_URL=wss://api2.pythnet.pyth.network
 export SERVER_URL=https://quorum-1.pyth.network,https://quorum-2.pyth.network,https://quorum-3.pyth.network
-export SECRET_KEY=/path/to/secret.key
+export SIGNER_URI=file:///path/to/secret.key
 export WORMHOLE_PID=H3fxXJ86ADW2PNuDDmZJg6mzTtPxkYCpNuQUTgmJ7AjU
 export RUST_LOG=INFO
 
@@ -60,7 +71,7 @@ You can provide multiple server URLs in the `SERVER_URL` environment variable by
 
 ### 🔑 Generate a Secret Key
 
-To generate a new secp256k1 secret key and write it to a file:
+To generate a new **armored OpenPGP secp256k1 secret key** and write it to a file:
 
 ```bash
 RUST_LOG=INFO cargo run -- generate-key --output-file .secret