Update default Jenkins file with comments

Jenkinsfile

@@ -2,7 +2,7 @@ pipeline {
     agent any
 
     tools {
-        maven 'Maven 3.9.9'
+        maven 'Maven 3.9.9' // Change this to the needed maven installation
     }
 
     environment {
@@ -25,6 +25,8 @@ pipeline {
             }
         }
 
+        // Uncomment this section to send notification to Discord. Replace <DISCORD_WEBHOOK_URL> with the webhook url.
+        // - Requirement: Discord Notifier plugin installed in Jenkins
         // stage('Notify Discord') {
         //     steps {
         //         script {