Add comment for reproducible builds

See https://maven.apache.org/guides/mini/guide-reproducible-builds.html

Author: garydgregory

pom.xml

@@ -77,6 +77,7 @@
     </dependency>
   </dependencies>
   <properties>
+    <!-- project.build.outputTimestamp is managed by Maven plugins, see https://maven.apache.org/guides/mini/guide-reproducible-builds.html -->
     <project.build.outputTimestamp>2024-08-14T23:15:56Z</project.build.outputTimestamp>
     <maven.compiler.source>1.8</maven.compiler.source>
     <maven.compiler.target>1.8</maven.compiler.target>