README does not show how to run background jobs

[arielj]

Branch/Commit:

Main branch

Expected behavior:

I want to see in the readme the needed steps to run the complete app.

Actual behavior:

The readme shows only the rails s server but says nathing about sidekiq.

I will abide by the [code of conduct] (https://github.com/rubygems/rubygems/blob/master/CODE_OF_CONDUCT.md)

[bronzdoc]

@FionaDL can you add documentation for this? thanks!