Download this.

Place in %AppData%\BetterDiscord\plugins.

If you have curl installed (included in Windows 10 versions 1803 and later) you can run the following command to download the file to the appropriate folder:

curl -L -o "%AppData%\BetterDiscord\plugins\BetterEmotes.plugin.js" https://github.com/Lombra/BetterEmotes/raw/master/BetterEmotes.plugin.js