added missing short description for newly added commands

core/src/main/resources/jenkins/model/Messages.properties

@@ -54,3 +54,5 @@ CLI.quiet-down.shortDescription=Quiet down Jenkins, in preparation for a restart
 CLI.cancel-quiet-down.shortDescription=Cancel the effect of the "quiet-down" command.
 CLI.reload-configuration.shortDescription=Discard all the loaded data in memory and reload everything from file system. Useful when you modified config files directly on disk.
 CauseOfInterruption.ShortDescription=Aborted by {0}
+CLI.shutdown.shortDescription=Immediately shuts down Jenkins server
+CLI.safe-shutdown.shortDescription=Puts Jenkins into the quiet mode, wait for existing builds to be completed, and then shut down Jenkins.