You can create an excel file or text file that contains the contents of the summary.
Basically you would have a single record/single column file that acts as a "datasource".
You could also simply put the text in Tableau using a variety of methods, such as the "Text" dashboard object.
Hope this helps!
So how does the "Text" object on the dashboard pick up the contents of the file, be it excel or text?
The "Text" object on the dashboard would be a copy/paste operation to insert.
The other method would be more dynamic if you expect it to change often.