r81 is the last release for Android 5.0.
r82 or newer is only for Android 5.1 - don't flash them on older Android versions.
fastboot flash boot boot_name_img
flash the .zip in the recovery
Official app support:
Got any questions that you couldn't find after searching?
Disclaimer to moderators:
Slight OT is fine, but when users decide to act stupid they should be dealt with with the appropriate means - its really annoying for me when OT turns crazy. Please put the warning/ban hammer anytime any of you think there's lack of respect and/or too much unwanted OT crap - but if it doesn't meet this criteria let the OT posts alone. Thank you.