[IMP] website_forum_doc: add clickable on tree view of forum.post 

Hello,
    I have improve code add default state on documentation post and it's clickable.
    Task : https://www.odoo.com/web#id=9016&view_type=form&model=project.task&action=327
    Pad : https://pad.odoo.com/p/r.D5cveSvTObgbLuIC
Thanks.