I couldn’t see it at first either. I had to clear my browser(s)caches (I had opened my admin panel in FF and IE)then because I use CloudFlare I cleared the cache there too, refreshed and only then could I see the snippet editor.
Where it says Snippet Editor, under the title and the URL there is a blank space or a space with some text, on the right side of it when you move your cursor over it there is a pencil for editing.
I am not impressed with this snippet editor at all.