docs: explain read-only simulation behavior in Interact tutorial

docs/build/smart-contracts/getting-started/deploy-to-testnet.mdx

@@ -129,6 +129,24 @@ The following output should appear.
 ["Hello", "RPC"]
 ```
 
+:::note
+
+You may also see a message like:
+
+```
+ℹ️  Simulation identified as read-only. Send by rerunning with `--send=yes`.
+```
+
+This is expected! The `hello` function is **read-only**—it doesn't modify any on-chain state. When the CLI detects a read-only function, it automatically runs it as a **local simulation** instead of submitting a transaction to the network. This means:
+
+- **No fees**: The simulation is free—no transaction is submitted to the ledger.
+- **Instant result**: The output you see (`["Hello", "RPC"]`) is already the correct result.
+- **Ignore `--send=yes`**: For read-only functions, the simulation already gave you what you need.
+
+The `--send=yes` flag is only needed for **state-changing functions**—those that write to contract storage. For those, the CLI first simulates the transaction (to estimate fees and check for errors), then you use `--send=yes` to actually submit and persist changes on-chain.
+
+:::
+
 :::info
 
 The `--` double-dash is required!