StackOverflow just announced a new Community Documentation feature, and there's already an Elm page up:
I think this has the possibility to fill a different purpose than the main Docs or the GitBook, mainly that it is very example oriented, and has the possibility to grow very large and detailed. It probably will overlap with the Community FAQ.
So while the Gitbook is meant to be read from start to finish, the SO docs are probably more a repository of examples, answers to the questions of "how do I accomplish thing X", where thing X can be something oddly specific, or even library specific, that we wouldn't want to delve into in the main docs.
I realise there's some risk of fragmenting the docs, but regardless of whether it's a good thing or not, people are likely going to contribute, and they already have. It's probably good to have this list oversee and contribute to examples, to ensure the resulting docs are high quality.
Happy documenting!
Joey