Add backt the HTDP book

README.md

@@ -162,7 +162,7 @@ All coursework under Core CS is **required**, unless otherwise indicated.
 
 Courses | Duration | Effort | Prerequisites | Discussion
 :-- | :--: | :--: | :--: | :--:
-[Systematic Program Design](https://learning.edx.org/course/course-v1:UBCx+SPD1x+2T2015) (alt: [part 1](https://www.edx.org/course/how-to-code-simple-data) / [part 2](https://www.edx.org/course/how-to-code-complex-data)) | 13 weeks | 8-10 hours/week | none | chat: [part 1](https://discord.gg/RfqAmGJ) / [part 2](https://discord.gg/kczJzpm)
+[Systematic Program Design](https://learning.edx.org/course/course-v1:UBCx+SPD1x+2T2015) [(textbook)](https://htdp.org/2023-8-14/Book/index.html) (alt: [part 1](https://www.edx.org/course/how-to-code-simple-data) / [part 2](https://www.edx.org/course/how-to-code-complex-data)) | 13 weeks | 8-10 hours/week | none | chat: [part 1](https://discord.gg/RfqAmGJ) / [part 2](https://discord.gg/kczJzpm)
 [Programming Languages, Part A](https://www.coursera.org/learn/programming-languages) | 5 weeks | 4-8 hours/week | Systematic Program Design ([Hear instructor](https://www.coursera.org/lecture/programming-languages/recommended-background-k1yuh)) | [chat](https://discord.gg/8BkJtXN)
 [Programming Languages, Part B](https://www.coursera.org/learn/programming-languages-part-b) | 3 weeks | 4-8 hours/week | Programming Languages, Part A | [chat](https://discord.gg/EeA7VR9)
 [Programming Languages, Part C](https://www.coursera.org/learn/programming-languages-part-c) | 3 weeks | 4-8 hours/week | Programming Languages, Part B | [chat](https://discord.gg/8EZUVbA)