Clarify annotation processor config with AspectJ

Closes gh-4847

spring-boot-docs/src/main/asciidoc/appendix-configuration-metadata.adoc

@@ -712,6 +712,26 @@ handling for collection types (that will be detected even if only a getter is pr
 annotation processor also supports the use of the `@Data`, `@Getter` and `@Setter` lombok
 annotations.
 
+[NOTE]
+====
+If you are using AspectJ in your project, you need to make sure that the annotation
+processor only runs once. There are several ways to do this: with Maven, you can
+configure the `maven-apt-plugin` explicitly and add the dependency to the annotation
+processor only there. You could also let the AspectJ plugin runs all the processing
+and disable annotation processing in the `maven-compiler-plugin` configuration:
+
+[source,xml,indent=0,subs="verbatim,quotes,attributes"]
+----
+	<plugin>
+		<groupId>org.apache.maven.plugins</groupId>
+		<artifactId>maven-compiler-plugin</artifactId>
+		<configuration>
+			<proc>none</proc>
+		</configuration>
+	</plugin>
+----
+====
+
 
 
 [[configuration-metadata-nested-properties]]