Add a section for Open Source GPTs

[Stefan R. Grotz]

I organize the prompts, actions and some of the knowledge files of my GPTs on GitHub. I can't be the only one. It would be nice if we could have a section with completely Open Source GPTs.

Here are two of mine:

• Open Data Germany
• EsperantoGPT

[Stefan R. Grotz]

I created a PR for this: #21

[Stefan R. Grotz]

Thanks!