Add custom or pre-defined informational note at the top of a Custom Tool

[Clubdebambos]

I would like to be able to add informational notes at the top of custom tools, either with Python or the Toolbox GUI, similar to what I see here for the Append tool where it says "This tool modifies the Target Dataset"

I want to add a customised informational note of my own at the top of a custom tool.

Or, a good start would be to add some default notes to choose from, like that in this example.

I know I can set Warning messages for parameters, this does not cover this idea as they are different. 

[AlfredBaldenweck]

I've thought about this a bunch recently, and I think it'd be a great addition to the functionality here.

[DuncanHornby]

You can add text, images and even hyperlinks to a script summary. With these set you or your user need only move the cursor over the blue ? in the circle to display it.