In the upper right-hand corner of the forum webpage, there is a search feature. Do a search on Nikon D810. There are numerous answers to your question.
Lightroom 5.5 is the latest version. If you don't want to wait for the next release, you can download Adobe DNG Converter 8.6RC which will transform your D810 NEFs into DNGs that the current version of Lightroom can use.
The above URL will evidently download both Camera Raw and the DNG Converter release candidates.