Riven vs Renekton

You pretty much straight up lose. You lose every trade quite easily and he has sustain.

All you can do is farm and punish him if he tower dives you.

You don't fight him early if he dashes towards you - you dash as well to activate your shield and negate part of his damage. You'll crush him late game though.

It's an odd matchup which tips in Renekton's favour.

In my experience, the person who initiates fights will typically lose. If Renekton initiates, Riven can stun and disengage. If Riven initiates, Renekton can turn it around and chase.

I'd probably recommend prioritizing farm and trade only when he engages. Try to shield his Q and W when he engages.

I'd probably recommend getting Black Cleaver relatively early (either first or second item). Ninja Tabi quite useful for mitigating his damage. A couple Doran's Blades early would be helpful for the additional bulk and sustain.

bend over and pray he starts falling off soon

Just AFK that's what I do if I have to lane against a counter.