Bind off 5 sts at beg of next row, then dec at armhole edge, [2sts] once and [1st] twice.
You bind off those 5 at the beginning of the row--that's the armhole edge.
Then work a row even.
On the next row, bind off 2 stitches at that same row.
Work a row even.
On the next two right-side rows, bind off one stitch at the armhole edge.