Update index.md

Author: jcbhmr

index.md

@@ -102,7 +102,7 @@ _TODO: Make sure this is up-to-date_
 
 You can view language-specific leaderboards on each language's competition page.
 
-## The challenge
+## 💪 The challenge
 
 Your mission, should you choose to accept it, is to write a program that retrieves temperature measurement values from a text file and calculates the min, mean, and max temperature per weather station. There's just one caveat: the file has 1,000,000,000 rows! That's more than 10 GB of data! 😱