feat: Day 9: Marble Mania (part 2)

Author: mariotacke

day-09-marble-mania/README.md

@@ -53,5 +53,11 @@ Here are a few more examples:
 
 **What is the winning Elf's score?**
 
+## Part Two
+
+Amused by the speed of your answer, the Elves are curious:
+
+**What would the new winning Elf's score be if the number of the last marble were 100 times larger?**
+
 ## References
 - https://adventofcode.com/2018/day/9