Rather than having text appear directly on your Onescreener page as a "Main Content" item, you can choose to add an icon that generates a pop-up window with your message/ biography/ updates in it. Here's how:
Starting at your navigation page, click on LINKS/ ICONS. Then click on the Add new link button.
Next, choose the About (!) icon from the Select content link menu and enter your text. When finished, click on the Add link button below.
Then, preview your page to ensure that the link has appeared, and click on it to view its content. You'll see that the pop-up window contains your text. Note that this can be updated at any time!
Lastly, go back to your navigation page and PUBLISH YOUR SITE so that the changes go live.