1. Install HTC Sync Manager
(Required because it packs in the drivers essential for PC to recognize the device)
2. Unlock your phone's bootloader
Follow the steps listed here : http://www.htcdev.com/bootloader
You need to select device model as "HTC One"(Don't worry, it all follows almost same steps)
3. Download and Install a custom recovery!
> Download your recovery exe file(I recommend it so that it doesn't causes any troubles for newbies) from here.
> Boot you phone into fastboot and run the exe file, it will install the recovery(CWM 18.104.22.168 as of the date of writing).
> Boot into recovery by selecting HBOOT(Select using Power button and scroll via volume keys)
4. Download and flash SuperSU!
> Download the latest SuperSU zip file from here!
> Place it in the root of your sd card(Internal or External, your choice)
> Boot into recovery and select "Install Zip from SD Card".
> Select where you kept the flashable zip(Internal/External storage)
> Select the file when it shows all your files and then select "Yes" to let it flash.
> After flashing completes, reboot!
> Use the wp_mod.ko module from here!
> Profit! You finally have a rooted HTC Desire 816! Yay!
@kinghunki for the initial recovery images.