I've used English terminology throughout.
1) Ch 21 + ch1 (for turning) in the colour you want to make the edging in.
2) 1tr in second ch from hook and each chain to end. (21 stitches) Ch2 and turn. 1tr in third stitch from hook and each st to end. Turn.
3) *Join in new colour, snip off old colour and leave ends. Ch1, 1tr in second stitch from hook and each stitch to end. Ch2 and turn. 1tr in third stitch from hook and each stitch to end. Turn.*
4) Repeat from *-* until you've achieved your desired length
(I used two 50g balls of both colours).
Make sure you end on the same colour you started with.
1) *YO. Miss a stitch. TR into next along from missed stitch. 4tr more into same stitch. Miss a stitch. DC into next stitch along from missed stitch.*
2) Repeat from *-* 4 times.
3) For other end (ie: end you started the scarf at): join in edging colour to first chain and repeat step 1) and 2)
Weave in all those ends and wear your scarf with pride!