When you add a stitch on the edge, it just becomes part of the rib pattern. So if for example your stitches so far are:
K5, P2, K5, P2
To increase one stitch at each end you could do kfb (knit into front and back of stitch) on the first stitch, then the K4, P2, K5, P1, pfb.
On the following row, which would be a wrong side row and using our example would normally be:
K2, P5, K2, P5
You would now have:
P1 (this is your new stitch), K2, P5, K2, P5, K1 (this is your second new stitch)
The next row, a right side row, would be:
P1, K2, P5, K2, P5, K1
Again, this is just an example, but does it help to see what you need to do??