cron: add alias page (#9388)

* cron: add alias page

* cron: remove trailing whitespace

* ripgrep: use standard alias description

* todoman: use standard alias description

pages/common/cron.md

@@ -0,0 +1,8 @@
+# cron
+
+> `cron` is a system scheduler for running jobs or tasks unattended.
+> The command to submit, edit or delete entries to `cron` is called `crontab`.
+
+- View documentation for the original command:
+
+`tldr crontab`