Old Man - Neil Young

Old Man - Neil Young

How is the musical notation inserted? I didn’t know that was possible.

Just by inserting any characters as text comments. You can use a unicode database app to search for any musical symbols (not all are permitted in iReal Pro). That works with any Android devices. I'm not sure about iOS, though. Keep in mind that text spacing can differ from devices brands. You might need to re-adjust the space between characters for proper display.