Update README.md

Author: josemoracard

exercises/016-century/README.md

@@ -20,6 +20,8 @@ century(2001)
 
 + Note that, for example, the 20th century began with the year 1901.
 
++ You may need to import the `math` module.
+
 + If you don't know how to start solving this assignment, please review the theory for this lesson: https://snakify.org/lessons/integer_float_numbers/
 
 + You may also try step-by-step theory chunks: https://snakify.org/lessons/integer_float_numbers/steps/1/