[skip ci] Automatically detect [cronjob] messages in your last commit (#5647)

* [skip ci] Automatically detect [cronjob] messages in your last commit
Signed-off-by: Nquicksilver <zhifeng.zhang@zilliz.com>

* [skip ci] Automatically detect [cronjob] messages in your last commit
Signed-off-by: Nquicksilver <zhifeng.zhang@zilliz.com>

* [skip ci] Automatically detect [cronjob] messages in your last commit
Signed-off-by: Nquicksilver <zhifeng.zhang@zilliz.com>

* [skip ci] Automatically detect [cronjob] messages in your last commit
Signed-off-by: Nquicksilver <zhifeng.zhang@zilliz.com>

build/ci/jenkins/NightlyCI.groovy

 #!/usr/bin/env groovy
 
+// When scheduling a job that gets automatically triggered by changes,
+// you need to include a [cronjob] tag within the commit message.
 String cron_timezone = "TZ=Asia/Shanghai"
 String cron_string = BRANCH_NAME == "master" ? "50 20,22,0,6,11,16 * * * " : ""