Add scheduled Job doc (#3847) [ci skip]

docs/backend/readme.md

@@ -11,6 +11,7 @@ items:
   - admin.md
   - previewing-emails.md
   - notification.md
+  - scheduled-jobs.md
 ---
 
 # Backend Guide

docs/backend/scheduled-jobs.md

@@ -0,0 +1,19 @@
+---
+title: Scheduled Jobs
+---
+
+# Scheduled Jobs
+
+As in the [Technical Overview](/technical-overview), We use [Heroku Scheduler](https://devcenter.heroku.com/articles/scheduler) for scheduled jobs. As the name suggests, this is for regularly recurring tasks that need to be run every day, week, month, year, decade, and century.
+
+Tasks are implemented in `dev.to/lib/tasks/fetch.rake`, typically in the form of:
+
+```
+task some_unique_task_name:, [optional_arg] => :environment do |optional_arg|
+  ... do your thing here ...
+end
+```
+
+You can explore the [official Heroku documentation](https://devcenter.heroku.com/articles/scheduler#defining-tasks) for defining tasks and read through tasks we have implemented for busting cache, awarding badges, and more.
+
+In your Pull Request, communicate with a DEV Core Team Member to discuss at what frequency and ensure your task is scheduled on Heroku once your code is reviewed, approved and merged.