add zenodo citation

README.md

@@ -9,8 +9,19 @@
 # Introduction to data science (for not yet scientists)
 Data Science course developed at the Düsseldorf University of Applied Sciences (HSD) and the Centre for Digitalization and Digitality (ZDD).
 
+## Access the online version of this book:
 For the rendered book use [this link](https://florian-huber.github.io/data_science_course/book/cover.html)!
 
+## Citation & pdf version of this book:
+A pdf version of this book can be found [on zenodo](https://zenodo.org/records/10074475)
+
+This book and all material used to create the book are freely available and can be used according to the CC license (BY-NC-SA 4.0).
+If you use (parts of) this book for your work, please cite the book as:
+
+*Huber, F. (2023).*  
+*Introduction to Data Science (for not-yet scientists).*  
+*v0.5, 2023, Zenodo. https://doi.org/10.5281/zenodo.10074475*
+
 ## Create new environment for this course (recommended)
 It is recommended to create a new environment for this course with many Python libraries that we will use in the Live Coding sessions. You can simply download the `environment.yml` file in this repository, or clone the repository using:
 ```