/etc/udev/rules.d/backlight-permissions.rules crashes the command line

[EphraimB]

I tried installing this: https://github.com/mjtice/MMM-Screendimmer but when I tried editing /etc/udev/rules.d/backlight-permissions.rules, the command line in putty crashed. Now the 7 inch Raspberry Pi display is booted up but it keeps showing the thinking _ repeatedly. I don’t know what do do. It keeps saying that /etc/udev/rules.d/backlight-permissions.rules isn’t found when trying to edit it now.