An unofficial version of Android 7.1 Nougat has made its way to the Google Nexus 5X by way of a custom ROM from Cyanogen Mod.
Cyanogen Mod has launched the CM14.1 ROM for the Nexus 5X and it gives the device the much needed update to Nougat. Bear in mind that this is a nightly build of the ROM and as such there may be things that are not working as they should.
If you want to go ahead and install the custom Nougat ROM onto your device you should first check that you have 80% battery life left and then back up the device. Make sure that you have enabled USB debugging and have a rooted device with TWRP or CWM installed. Once you have done, this you can then follow the guide below, to install Nougat onto your device.
You are going to need the CM14.1 ROM along with Google Aps and these should be downloaded to the SD card of your handsets.
When you have them on the SD card you can disconnect it from the computer and then when you turn on your handset you can go into recovery by holding the volume up, down and recovery buttons. Now you should see Bootloader or Fastboot and using the keys for navigation and the power button for choosing you can go to Bootloader and Recovery.
Choose backup and do a Nandroid backup and then head to the main menu and choose to wipe the data by wipe data/factory reset and then go ahead and wipe the cache partition along with delvik cache.
Find where you downloaded the ROM on your SD card and install it and then repeat the same process to install GApps. Finally you can reboot your handset and you will have Android Nougat installed.