Documentation: create new merge request permissions

According to https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/user/permissions.md neither Guests nor Reporters have access to create merge requests.

It also says "On public and internal projects the Guest role is not enforced."

From this statement & table, it would see that for public projects, users have Reporter access, and should be unable to create merge requests.

Can someone confirm the actual behavior, and update the docs to match?