How do I add a comment as of why I editted a page?

As an example: I edited the page of the Sanctuary Guardian because a guy wrote that the rusted iron ring is a prequisite to move in the water, which is false. So I removed it. I would have like to add a comment to guys that check my edit to tell: "The Rusted Iron Ring is not required."

There's a small arrow beside the save button, click that to either save with comment, save without leaving the editor, or to switch between wiki code and wysiwyg editor.