Add context on auto-relayer for devnet

Adding explainer for auto-relayer

Author: zainbacchus

pages/stack/interop/tools/devnet.mdx

@@ -74,6 +74,13 @@ Alternatively block explorers per chain can be found below:
 *   Interop devnet 0: [Blockscout](https://optimism-interop-alpha-0.blockscout.com/), [Routescan](https://420120000.testnet.routescan.io/)
 *   Interop devnet 1: [Blockscout](https://optimism-interop-alpha-1.blockscout.com/), [Routescan](https://420120001.testnet.routescan.io/)
 
+## Superchain interop transaction relayer 
+
+Superchain cross-domain messages require two transactions. The first transaction creates an initiating message on the source chain. The second transaction creates an executing message on the destination chain.
+
+To simplify user experience, the Superchain interop devnet has a relayer running that will automatically execute the second transaction. If your transaction does not get relayed or you prefer to relay manually you can do so by following this [tutorial](https://docs.optimism.io/stack/interop/tutorials/message-passing#implement-manual-message-relaying). 
+
+
 ## Next steps
 
 *   Review the [Superchain Interop Explainer](/stack/interop/explainer) for answers to common questions about interoperability.