How to Create "Portal-ext.properties"

• Type: Task
• Status: Backlog
• Priority: Minor
• Resolution: Unresolved
• Fix Version/s: 7.0.x, 7.1.x
• Component/s: Core Infrastructure
• Labels: None
• Type of Documentation: Developer: Application Development

Hello , I'm new for liferay and I try to development liferay in Server Linux Ubuntu.
I don't understand how to create file "Portal-ext.properties"
Please, let me know how to do it.
Thanks