Unzip the archive for your operating system and copy that directory to the plugins directory of your Xournal++ installation (Shared resources folder or Config folder1).
To get the plugin custom icon to show up when adding the toolbar icon for a plugin, copy the .svg file in the plugin directory to a GTK supported icon location (e.g. $HOME/.local/share/icons/ or /usr/share/icons/ on Linux and %LOCALAPPDATA%\icons\ or %PROGRAM_FILES%\Xournal++\share\icons\ on Windows).
Windows:
If the plugin directory contains .dll files this additionally requires adding the directory to the PATH environment variable so that the contained .dll files can be found when loading main plugin .dll file from Lua in Xournal++.
To do this search for Edit Environment variables for your account in the Windows search, click Environment Variables, on the upper list of the User variables click the existing entry Path and add a new directory path of the plugin directory (e.g. %LOCALAPPDATA%\xournalpp\plugins\PLUGIN_NAME).
After applying the changes Xournal++ needs to be restarted.
Full Changelog: https://github.com/AnonymerNiklasistanonym/inkpath/commits/v0.2.1