adding comment to pom.xml

Change-Id: I7739d1be728123edf3872e4e4794f9a5c60f8704
diff --git a/pom.xml b/pom.xml
index 8c65299..3005cea 100644
--- a/pom.xml
+++ b/pom.xml
@@ -531,6 +531,7 @@
                     </configuration>
                 </plugin>
 
+                <!-- This version needs to be updated manually when changes are made to onos-maven-plugin -->
                 <plugin>
                     <groupId>org.onosproject</groupId>
                     <artifactId>onos-maven-plugin</artifactId>