add textbook

README.md

@@ -31,6 +31,28 @@ properly. Some idioms are listed on [this
 page.](https://github.com/zhijieshi/cse3666/blob/master/rv-examples/risc-v-idioms.md)
 In addition, good code should be easy to read.
 
+## Textbook
+
+The textbook is  
+
+    David A. Patterson and John L. Hennessy. Computer Organization and Design
+    RISC-V Edition: The Hardware Software Interface (The Morgan Kaufmann Series in
+    Computer Architecture and Design) 2nd Edition, Morgan Kaufmann. Dec 2020.
+    ISBN-13: 978-0128203316.
+
+Note that it is the second edition (NOT the first edition) of the RISC-V
+version. The UConn bookstore should have the correct edition. Here is the
+textbook on Amazon.com. 
+
+[Link to the textbook on Amazon.com](https://www.amazon.com/Computer-Organization-Design-RISC-V-Architecture/dp/0128203315/)
+
+The following is the page on the publisher's website that provides additional
+contents like online chapters. You can also download the reference card (in the
+textbook) from there. Search "RISC-V Reference Data" on the page.
+
+[Additional resources from the
+textbook](https://www.elsevier.com/books-and-journals/book-companion/9780128203316)
+
 ## File storage
 
 **Important:** Save your files to cloud storage like OneDrive. Local