docs(clean_the_list): add line after each bullet point

subjects/devops/clean_the_list/README.md

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 Create a file `shopping.py` that contains a function `clean_list` which takes in a list of strings and performs the following operations on each list item:
 
 - Removes all spaces before and after (but not between words).
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 - Capitalizes the first letter (first letter only, other ones should be to lowercase).
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 - Adds its index number before a separator `x/ `.
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 - An empty list as input should return an empty list as output.
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 - And don't forget the milk! (add it at the end of the list if missing).
 
 ### Usage