First off, ADC nidalee is not the worst build ever ( Never try magic penatration garen :D). Some might say adc nidalee is horrible because none of her abilities scale with AD. This is somewhat true. I'll go into detail later. For now, I'll list some pros and cons for ADC nidalee
( First guide, so i don't have any helpful pictures or decorative stuff)

Pros

Great pushing potential
You are often underestimated
Takedown deals insane amounts of damage ( especially if they are low and are hunted)
Can take down towers quickly

Cons

No CC
Abilities don't scale with AD (Except Takedown)
Can't trade well with other ADC's

Here are some basic skill combos you can use as ADC Nidalee. I recommend using these combos at lvl 6+, so that cougar form deals more damage, but up to you.

This combo is great for quickly suprising your enemy with quick damage. They usually aren't expecting you to use cougar form as an ADC. I don't use swipes, because you remain in place when you use it so you have to chase them again to use takedown.

Javelin Toss--->(MAke sure they are hunted)Aspect of Cougar--->Pounce (onto enemy)--->Takedown---->Pounce (back away)---> Aspect of Cougar ( back into human)---> Primal Surge--->As many AA as you can.

Another great combo if they happen to walk on your bushwhacks in the brush. I use swipes here cause you are in brush, you have bonus speed.

Javelin Toss( easy to land since they are revealed and no minions in way)---> Pounce---->Swipe--->Pounce---->Takedown---->Aspect of COugar---->Primal Surge----> AA

Useful when jungler comes and/or if enemy is stunned, rooted, or movement impaired.

Javelin Toss---> Primal Surge---->AA again and again

Quick small burst

Start in brush---->Javelin Toss---> come out of brush---> AA---> run back into brush---->AoC---->Pounce away