Requires "Jira administrator" permission
Create a Calendar using this guide - Create, Add Existing and Edit calendars
Add your team's Jira group as a User or Admin in the calendar permissions section.
Add your Calendar as Default for you team.
Go to System->Apps->DOITBETTER CALENDAR->Default calendars
Then select "Add default calendars."
Choose the calendar you want to add and the group you want it added to.
If the "Always add" checkbox is not selected, the default calendar will only be added to users who have no calendars; otherwise, it will be added to all users.