The main page area is a Google Doc, embedded in this page. It is editable in box below (desktop only), or by editing this Google Doc.
[note 2018-11-06: editing within page is reported not working in some cases - e.g. on Mac Chrome browser, when you are logged in to Google). You may see error message (press CANCEL), or Google Doc may not load. Try logging out of Google, using a different browser in which you are not logged in, or edit the Google Doc directly]