I would like to point that, when you are with the mouse cursor over the documentation of this macro, a small blue “Source” button appears in the bottom-right.
Clicking it will give you the source code for that documentation, it will be the triple quoted string highlighted in yellow. You can then go to the top of the document, click in the “Tree: […]” dropdown below the “Code” tab and select “master” (in sub-tab branches) the page will reload. Now you can click the small pencil at right of the buttons “Raw” “Blame” (if it does not appear it is because you are not logged in Github, log in and come back there; if its not clickable and its hovertext is “You must be on a branch…” then you did not select “master” in the previous step).
Now you can go back to that line of the file and edit it (the file will be a writable form field now), unfortunately the lines will not be highlighted anymore so you need to search for it (or remember the line number). After the edit you can write a small title and description for your contribution (in the page bottom) and press “Propose changes”. This will create a PR (Pull Request) that will be analyzed by the Julia maintainers and if approved will change the documentation for the next Julia version.