@hyphenfi,
You can place an icon (info or question-mark) to the top-right of the chart & pass description as title attribute of the icon. The description will be shown in a tooltip on hovering the icon. Please take a look at this JSFiddle for an example.

Also, you can convert it to a JavaScript function so that you can add information for multiple charts. Please refer to this JSFiddle for an example on the same.
—
Vishwas R
Team CanvasJS