These need to be separated from the main body of the text, and are best set with a smaller size and possibly event a different typeface and colour. The idea of any notes is that it is supplementary information and it is entirely optional that the reader even bothers to look, so setting in a style that does not distract from the flow of the reading experience is important.
Sidenotes Peter Kahrel
Footnotes and Endnotes, PDF, Note (Typography)
Footnotes in Two Columns (Microsoft Word)
Footnotes, Endnotes, Sidenotes and Popup Notes
Use footnotes and endnotes in Pages on iPad – Apple Support (UK)
Convert Fixed Notes to Dynamic Footnotes/Endnotes
PagetoScreen the web site where Chris Jennings displays his stuff
Sidenotes Peter Kahrel
Footnotes, Endnotes, Sidenotes and Popup Notes