The main README INSTALL instructions should cover installing pyscFilteredViewer under a normal installation of Notepad++ and PythonScript, such that the pyscFilteredViewer scripts go in the %AppData%\Notepad++\plugins\config\PythonScript\scripts\pyscFilteredViewer\ directory.
If you have a "portable" version of Notepad++, where the doLocalConf.xml file is in the same directory as notepad++.exe, then PythonScript will not look in the %AppData% hierarchy for scripts. Instead, it will look in <notepad++.exe directory>\plugins\config\PythonScript\scripts\ , so you will want to unzip the pyscFilteredViewer scripts into <notepad++.exe directory>\plugins\config\PythonScript\scripts\pyscFilteredViewer\ .
A note on "user scripts" vs "machine scripts": PythonScript hsa two locations for its scripts, which it calls "user scripts" and "machine scripts". The user scripts are intented to be unique per user of a computer, whereas the machine scripts are common to all users of that computer. The above instructions will put the scripts into the "user scripts" section.
In the main Plugins > PythonScript > Scripts menu, you won't see any difference between the two locations. If you go to Plugins > PythonScript > Configuration..., however, the dialog will only show you one or the other, depending on the radio-button selection at the top.
If you want the scripts to go in the "machine scripts" location, so that they are available to all users with an installed copy of Notepad++ (usually in the %ProgramFiles% or %ProgramFiles(x86)% hierarchy) then unzip into <notepad++.exe directory>\plugins\PythonScript\scripts\pyscFilteredViewer\ (note that this version doesn't have the \config\ in the path).