Add URL for adding remote upstream

Description

On the following page:
https://github.com/pixl8/Preside-CMS/blob/stable/support/docs/docs/03.contribguides/01.buildfromsource/page.md

Update the "Keeping your fork up to date" section with the git URL for core Preside.

Assignee

Niall

Reporter

Niall

Labels

None

Accepted

Yes

Fix versions

Priority

Medium
Configure