Not Updated For Current Season
The runes are pretty straight forward.
The Movement Speed and the Attack Speed quints work well with Bear stance and Tiger stance respectively, along with the attack speed marks.
Scaling HP seals give him a good cushion of HP in the mid to late game. this could be interchangeable with Scaling Armour but you should really never go flats as there will be a fair bit of farming the jungle for the early game to get sated.
CDR gives you a good early game to get through your clears with great sustain from getting Turtle more often, and the remaining Scaling MR is just to increase mid to late game tankiness.