[doc] Adds a short section on how to launch a blog based on the packages cubicweb and cubicweb-blog.
Needs review and renaming to follow convention if content is approved.
Add some entities
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As manager, you can access to entity creation forms by using the `site management`_ page.
.. _`site management`: manage
As regular user, the index page or the action box may propose some links to create entities according to the context.