You may create a custom field for that purpose, which is really easy.
In example, you may create a dropdown menu with the values you want.
Just go to:
https://<YOURS>.atlassian.net/secure/admin/ViewCustomFields.jspa
and click on 'Add custom field' on the top right corner.
Choose a type like "Single select" field and follow the wizard.
It looks like you're new here. Sign in or register to get started.