Click the [+] symbol at the bottom of the wiki page. This creates a gray "factory" at the end of the story.
Text: Double-click the gray to open the simple text editor. Proceed as you would to Add Text to existing paragraphs.
There are at least three text editors available. On is a text editor plug in, another is an HTML plugin, and the third is a markdown plugin.
Ward Cunningham prefers the text editor plug in that is activated when the + is clicked to open the factory and you click at the top of the grey space and begin typing in the window that opens.
I prefer the Markdown plugin for additional formatting.
I suppose that if you know HTML markup you might prefer HTML. The reader cannot tell unless they double click on the paragraph and then click Control-I for "information".