Add What's New Onboarding Item

https://trac.torproject.org/projects/tor/ticket/31660#comment:20

""" We should have something included in the 9.5 release onboarding for the new features. Antonela and I decided we can have one new entry named "What's New" (following Mozilla's new onboarding experience). This entry simply has a link to a webpage where new features are described.

The webpage is currently being developed at ​https://www.torproject.org/releases/tor-browser-95/ """