add license of Interpretable ML

books/free-programming-books-subjects.md

@@ -421,7 +421,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Gaussian Processes for Machine Learning](https://www.gaussianprocess.org/gpml/) - Carl Edward Rasmussen, Christopher K.I. Williams
 * [IBM Machine Learning for Dummies](https://www.ibm.com/downloads/cas/GB8ZMQZ3) - Judith Hurwitz, Daniel Kirsch
 * [Information Theory, Inference, and Learning Algorithms](http://www.inference.phy.cam.ac.uk/itila/) - David J.C. MacKay
-* [Interpretable Machine Learning](https://christophm.github.io/interpretable-ml-book/) - Christoph Molnar
+* [Interpretable Machine Learning](https://christophm.github.io/interpretable-ml-book/) (CC BY-NC-SA) - Christoph Molnar
 * [Introduction to CNTK Succinctly](https://www.syncfusion.com/ebooks/cntk_succinctly) - James McCaffrey
 * [Introduction to Machine Learning](https://arxiv.org/abs/0904.3664v1) - Amnon Shashua
 * [Keras Succinctly](https://www.syncfusion.com/ebooks/keras-succinctly) - James McCaffrey