Update README.md to point to current web page

Author: dvanhorn

README.md

@@ -6,7 +6,7 @@ University of Maryland, College Park.
 
 The current instance of this course is:
 
-* http://www.cs.umd.edu/class/fall2022/cmsc430/
+* http://www.cs.umd.edu/class/spring2023/cmsc430/
 
 Copyright © David Van Horn and José Manuel Calderón Trilla and Leonidas Lampropoulos