Add downloaded extension to KNIME

I might be overlooking things, but how do I add an extension that I downloaded?
I found the way to add a downloaded/archived update site, but this doesn’t seem to work on this extension.

Looking for a way to use this extension from Github;

Hi @chrisvdberge,

The archive that you have download does not actually contain compiled code that could be used with KNIME.

To use these nodes you’ll have to set up an environment as described in knime-sdk-setup and, additionally, import the the archive contents as existing project into Eclipse. Starting KNIME Analytics Platform from within your Eclipse will enable you to use those nodes. Alternatively, you should be able to export the nodes and use them with an existing KNIME Analytics Platform installation by dropping the JAR into the plugins/ folder of your installation.