As the rom is new and no one yet test it so we request your to test it out and report in comment section.As this is first cm13 nightly there may be bugs in it.I refer your to make backup of your current rom before flashing this rom.So Lets start the guide on How to install Official Cm13 rom on Huawei Nexus 6P.
1.Make sure you have Unlocked bootloader.
2.Your device must have custom recovery (TWRP) to install CM13 rom in it.
3.Always make backup of Current rom Before flashing any rom in your device.
#How to install official Cyanogenmod 13 rom in Nexus 6P
1.Download official CM 13 nightly for nexus 6P.and the appropriate Gapps 6.0 package
from link given below Copy it in your in your device.
2.Now place the Official Cyanogenmod 13 rom and gapps 6.0 zip file in sd card.
3.Now reboot to Recovery mode.
4.Then flash CM13 rom and Gapps 6.0 from recovery in it.
5.Now Clear cache and Clear Data.
6.Reboot your device.Done! you just flash Official cyanogenmod 13 rom in your Nexus 6P