Clarify grading breakdown in README

Author: alanedelman

README.md

@@ -90,7 +90,7 @@ Final Project presentations : we may have some done by video and some in class
 Final Project reports due: May 11
 
 # Grading: 
-25% problem sets,  25% quizzes,  10% for the final project proposal, and 40% for the final project. Problem sets and final projects will be submitted electronically.
+25% problem sets (approximately every two weeks or fewer),  25% quizzes (planned for every second wednesday),  10% for the final project proposal, and 40% for the final project. Problem sets and final projects will be submitted electronically.
 
 # HW
 |#|HW| Due Date |