Added documentation about job scheduling

refs https://github.com/TryGhost/Ghost/issues/12402

- Adds examples on how to queue regular "immediate" and reccuring "scheduled" jobs

ghost/job-manager/README.md

@@ -1,5 +1,7 @@
 # Job Manager
 
+A manager for tasks that have to be performed asynchronously, optionally recurring, scheduled or one-off in their nature.
+
 ## Install
 
 `npm install @tryghost/job-manager --save`
@@ -11,6 +13,31 @@ or
 
 ## Usage
 
+```js
+const JobManager = require('@tryghost/job-manager');
+
+const logging = {
+    info: console.log,
+    warn: console.log,
+    error: console.error
+};
+
+const jobManager = new JobManager(logging);
+
+// register a job "function" with queued execution in parent event loop
+jobManager.addJob(printWord(word) => console.log(word), 'hello');
+
+// register a job "module" with queued execution in parent even loop
+jobManager.addJob('./path/to/email-module.js', {email: 'send@here.com'});
+
+// register recurring job which needs execution outside parent event loop
+jobManager.scheduleJob('every 5 minutes', './path/to/jobs/check-emails.js', {}, 'email-checker');
+
+// register recurring job with cron syntax running every 5 minutes
+// job needs execution outside parent event loop
+// for cron builder check https://crontab.guru/ (first value is seconds)
+jobManager.scheduleJob('0 1/5 * * * *', './path/to/jobs/check-emails.js', {}, 'email-checker-cron');
+```
 
 ## Develop
 
@@ -36,4 +63,4 @@ Follow the instructions for the top-level repo.
 
 # Copyright & License 
 
-Copyright (c) 2020 Ghost Foundation - Released under the [MIT license](LICENSE).
+Copyright (c) 2020 Ghost Foundation - Released under the [MIT license](LICENSE).