[add]website_forum :add tour for forum.

Website_forum : Add a tour for website forum

Task: https://www.odoo.com/web#id=9330&view_type=form&model=project.task&menu_id=3942&action=327
Pad: https://pad.odoo.com/p/r.ng9HB6K2JCzYKLoi
What's the purpose of that ?