Add code comment for CONTAINER_REUSE exit code

Author: olpaw

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/util/ExitStatus.java

@@ -40,6 +40,7 @@ public enum ExitStatus {
     DRIVER_TO_BUILDER_ERROR(21),
     WATCHDOG_EXIT(30),
     REBUILD_AFTER_ANALYSIS(40),
+    // podman can exit 125 if container does not need building
     CONTAINER_REUSE(125),
     MISSING_METADATA(172),
     UNKNOWN(255);