How make a Panel Plugin with writing content to site.yml

Heya,

I am new to Plugins and try to make a Panel Plugin for Kirby 3 which writes and reads content from site.yml. Is there some how to or a sample Plugin to do this stuff? I tried to make it like normal field plugin like in the video of bastian.

If someone has a simple sample i would appreciate.

thank you

Regards Raphael