Clarify "Ready for Capella" (sigp#4095)

## Issue Addressed

Resolves sigp#4061

## Proposed Changes

Adds a message to tell users to check their EE.

## Additional Info

I really struggled to come up with something succinct and complete, so I'm totally open to feedback.

beacon_node/client/src/notifier.rs

@@ -460,7 +460,11 @@ async fn capella_readiness_logging<T: BeaconChainTypes>(
 
     match beacon_chain.check_capella_readiness().await {
         CapellaReadiness::Ready => {
-            info!(log, "Ready for Capella")
+            info!(
+                log,
+                "Ready for Capella";
+                "info" => "ensure the execution endpoint is updated to the latest Capella/Shanghai release"
+            )
         }
         readiness @ CapellaReadiness::ExchangeCapabilitiesFailed { error: _ } => {
             error!(