cli: add explaining text for graphite.messages

lib/cli/cli.js

@@ -1307,6 +1307,8 @@ export async function parseCommandLine() {
     .option('graphite.messages', {
       default: ['pageSummary', 'summary'],
       options: ['pageSummary', 'summary', 'run'],
+      describe:
+        'Define which messages to send to Graphite. By default we do not send data per run, but you can change that by adding run as one of the options',
       group: 'Graphite'
     })