Make plugin appear in Desktop Effects settings

Hello. I am trying to get into developing a plugin. First step for me is to get the example plugin working.

This is the example plugin:

I did the standard install procedure (cd build, cmake .., make, sudo make install), and it is now working. I can see the logs in journalctl.

However, I cannot find much information on having this plugin listed under Desktop Effects. Editing metadata.json alone is not enough. How can I add this so that user can toggle it in the settings? Thank you.