How to edit community documentation?

In the Community Documentation there is an article on Installation. As the page information shows, I wrote much of it back in 2015 when Windows 8 was still what came with most computers. Now Windows 10 is on the typical new machine, I have just installed 16,04 alongside Windows 10 and can state that the Ubuntu document needs a little updating. When I go to the document it says in the upper left, "Login to edit". So I login, but then It says "Immutable page" and I cannot make the needed changes. So it seems outdated information will be preserved, but how can I explain how to install Ubuntu 16.04 (the current LTS version) alongside Windows 10?

I get the impression that the whole community documentation system has changed but can find no explanation of the new system.

The "official documentation" on installation is enough to frighten almost anyone away from Ubuntu, so the community documentation is essential. How can I contribute?

Thanks for your help.