In order to add your statement, you will have to print and mail your tax return.  You can't attach general footnotes to the electronic returns, unfortunately.  The IRS does not allow general notes from taxpayers for electronic returns.  And in fact, they don't really want any general footnotes attached... if there is anything unusual on your tax return about business expenses, they will ask for it if necessary. Otherwise, you don't have to send it.

Note: The IRS has very specific attachments that are required to be mailed while sending the actual return electronically. They are listed on Form 8453 (link below). The IRS specifically states: "Do not attach any form or document that is not shown on Form 8453 next to the checkboxes. If you are required to mail in any documentation not listed on Form 8453, you cannot file the tax return electronically."

https://www.irs.gov/pub/irs-pdf/f8453.pdf