Notifications are essentially another API for end users, but
it can be hard to find the list of existing notifications or
their samples which are buried deep down via contributors >
technical reference deep dive > notitfications. If I'm an
end user, I'd like to just see them in the same set of links
on the main page as the API, under the "For End Users" section.
Change-Id: If3ca21b080d06a291ed27c9bcd84a566164c3b70
beac1529fd