generate README.md for reverse string via configlet

exercises/reverse-string/README.md

-# Reverse String
+# reverse-string
 
-For example: input: "cool" output: "looc"
+Reverse a string
+
+For example:
+input: "cool"
+output: "looc"
 
 # Running the tests
 
 
 in your terminal.
 
+## Source
+
+Introductory challenge to reverse an input string [https://medium.freecodecamp.org/how-to-reverse-a-string-in-javascript-in-3-different-ways-75e4763c68cb](https://medium.freecodecamp.org/how-to-reverse-a-string-in-javascript-in-3-different-ways-75e4763c68cb)
+
 ## Submitting Incomplete Solutions
 
-It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.