Add a note about `onbeforeunload` custom msg unsupported
Add a note about `onbeforeunload` custom msg unsupported

phanan/koel,mikifus/koel,mikifus/koel,phanan/koel,X-Ryl669/kutr,mikifus/koel,alex-phillips/koel,alex-phillips/koel,alex-phillips/koel,X-Ryl669/kutr,X-Ryl669/kutr,phanan/koel