Release notes: dead internal links

[deining]

Hi,

I just read though the release notes of picocli 4.1. Great work, especially the PropertiesDefaultProvider comes in very handy, I will definitely use it!

Reading the release notes,
https://github.com/remkop/picocli/releases
I realized that there are three dead internal links at the very beginning of the document:

The library now provides functionality that previously required custom code:
**PropertiesDefaultProvider**
**AutoComplete.GenerateCompletion**
**... **

Maybe you can fix this.

Thanks for for continuos work on picocli! Keep up the good work!