Ult when in range to aa. Proc first vital or q for first vital.
Use nimbus movespeed and ult movespeed to proc 2nd vital (preferably one closest to the wall to prevent them guarding that vital and forcing them to kite back or rush to other side of lane to protect that vital with a wall).
Use ult movespeed from proccing 2nd vital and your 2nd q to proc 3rd vital. Also, your 2nd and 3rd hits should have your e active to apply a slow to your opponent - further reducing their ability to kite you.
It has now been approximately 2-3 sec and you've procc'ed 3 vitals. Maybe 4 sec if you had to riposte an opponent's cc. If that's the case though, they are stunned and you can have an easier time hitting the 4th vital.
Hit 4th vital or... if they've managed to reach a wall, enjoy 4-6 sec of whaling on them with autos while they can't turn around to face you - lest they expose their last vital.
Congrats, you just demolished their hp bar.
Also... fiora is hard to trade against early in lane due to her q-poke on a low cd and the movespeed it gives her for hitting a vital thanks to her passive. A few champs can catch her after she pokes them and trade damage back; others cannot. The extra movespeed nimbus would provide for hitting someone with her q would be enough for a skilled fiora to probably dodge beyond the range at which those few opponents can retaliate by using their gapcloser or cc (such as darius pull) to catch her in turn. Thus, she has even better harass against which opponents should no longer stand a chance of retaliating properly.
Thus... nimbus should be sleeper op on fiora. Now if it's a keystone (I haven't looked), it probably won't be worth it, but for a lower tier rune, it will be very strong for more skilled players. Just as the higher you go, the stronger riven is... because people make better use of her ability to dive in, do some damage, and leave her opponents no chance to fight back against that poke - at best they trade into her shield. This is basically the same concept that fiora q-poke will be with nimbus. Sure low elo people won't notice much difference because we aren't fast enough with our combos and most players here only notice raw damage and stats, but I will bet plat or for sure diamond plus people will notice and it will be a niche pick. Not for every player, but appreciated by some and very good for those who use it well. Just as conqueror vs pta debate with renekton exists.