Add a list of guides in readme

README.md

 # Jupyter Tutorials
 
-This is a collection of tutorials for Jupyter Notebooks.
+This is a collection of guides for Jupyter Notebooks and [JupyterHub](https://jupyter.hs-bochum.de).
+
+- [How to use university's JupyterHub?](jupyterhub.md)
+- [How to launch gradio apps?](gradio.md)
+- [How to get graphic output of gymnasium environments?](gym-graphic-output.ipynb)