update bibtex

Author: justinsalamon

book/appendix/cite_this.md

@@ -0,0 +1,15 @@
+# Cite this Book
+
+If you wish to reference this book in your own work, we ask that you 
+use the following `bibtex` entry:
+
+```
+@book{opensourceseparation:book,
+	Author = {Ethan Manilow and Prem Seetharman and Justin Salamon},
+	Month = Oct.,
+	Publisher = {https://source-separation.github.io/tutorial},
+	Title = {Open Source Tools \& Data for Music Source Separation},
+	Year = 2020,
+	Url = {https://source-separation.github.io/tutorial}
+}
+```