This camera is very new, so you have to until the next version of LR is released—one that has support programmed into it.
The other thing you can do is use the DNG Converter 8.6 release-candidate available at Adobe Labs and convert you NEFs to DNGs and those DNGs will be recognized by the older LR version.
Look at the CS6 download for ACR 8.6 RC at Adobe Labs: http://labs.adobe.com/
Keep in mind that this is a pre-release program and things may change before the final release so your photos may look different at that time.
Also, this version of DNGC 8.6 RC doesn’t recognize the new 9MP Small Raw mode from the D810 so you’ll have to shoot full-res 36MP images to work with them in LR. Adobe has said this will be corrected in the final versions of the products, probably in a few weeks.