fix(4): make example consistent (#326)

Author: ndrpnt

aep/general/0004/aep.md.j2

@@ -42,7 +42,7 @@ For protobuf, use the [`google.api.resource`][resource] annotation:
 
 ```proto
 // A representation of a user event.
-message Topic {
+message UserEvent {
   option (google.api.resource) = {
     type: "user.example.com/user-event"
     singular: "user-event"