Q. How do I add a descriptive or informational footnote to my paper using Chicago Style?

The Chicago Manual of Style calls this kind of footnote "Substantive notes." 

From the Chicago Manual of Style, section 14.39:

Substantive, or discursive, notes may merely amplify the text and include no sources. When a source is needed, it is treated as in the example in section 14.38 or, if brief and already cited in full, may appear parenthetically, as in the following example:

1. Ernst Cassirer takes important notice of this in Language and Myth (59–62) and offers a searching analysis of man’s regard for things on which his power of inspirited action may crucially depend.

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