This is a community wiki and it grows with contributions from people like you.
On every page, there’s a link in the bottom right corner, it takes you to the source code of the page at github. Once there and logged in, you can edit the file online.
The easiest way to contribute is to use the Editor, but then you won’t receive credits and currently you can’t always submit. edit
This again requires you to have a github account, to edit everything on your computer locally, you need to fork this repository, commit your changes and submit pull requests. There’s an extensive guide which you should read in any case.