Tooltips are what I want, except for the fact that they only work when you are hovering over data, I want a text box that says help or documentation and once you hover over it the tooltip pops up with your information.
This functionality does not currently exist--I would definitely add it to the Ideas section though!
One way to maybe to do this though would be to place two worksheets on a dashboard together. The one worksheet would be full of your data. The second worksheet would simply have a calculated field that would say whatever was desired "Help" or "More Information Here"--then add the tool tip to this.
Hope that helps!