Update README.md

Author: tommygonzaleza

exercises/012-tens_digit/README.md

@@ -16,7 +16,9 @@ tens_digit(1234)
 
 ## Example input 2:
 
+```py
 tens_digit(179)
+```
 
 ## Example output 2:
 
@@ -26,4 +28,4 @@ tens_digit(179)
 
 + If you don't know how to start solving this assignment, please, review a 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/
++ You may also try step-by-step theory chunks: https://snakify.org/lessons/integer_float_numbers/steps/1/