Update README.md

Author: abhijithasokan

README.md

@@ -2,4 +2,4 @@ Instructions
   1. Add your cookie in `aoc_cookie.json` file 
   2. Edit `2020/template.py` (need to give correct year & day of challenge to submit)
   3. Write solution for level 1 in `solve_l1` and for level 2 in `solve_l2`
-  4. Run the script. If the above function return non-`None` values (`None` values for not submitted), script will ask for your confirmation before submitting the solution.  
+  4. Run the script. If the above functions return non-`None` value (`None` values are not submitted), script will ask for your confirmation before submitting the solution.