Add extra note about workload restart for proxy config (#2009)

Author: howardjohn

mesh/v1alpha1/istio.mesh.v1alpha1.pb.html

@@ -313,6 +313,8 @@ message Topology {
 // This is different than a deep merge provided by protobuf.
 // For example, `"tracing": { "sampling": 5 }` would completely override a setting configuring a tracing provider
 // such as `"tracing": { "zipkin": { "address": "..." } }`.
+//
+// Note: fields in ProxyConfig are not dynamically configured; changes will require restart of workloads to take effect.
 message ProxyConfig {
   // Path to the generated configuration file directory.
   // Proxy agent generates the actual configuration and stores it in this directory.