improve Caeser Cipher instructions

exercises/caeser_cypher/problem.md

@@ -1,24 +1,34 @@
 # Caesar Cipher
 
-The Caesar cipher, also known as a shift cipher, is one of the simplest forms of encryption. It is a substitution cipher where each letter in the original message (called the plaintext) is replaced with a letter corresponding to a certain number of letters up or down in the alphabet.
+The Caesar Cipher is a type of 'shift cyper' where each letter of the original
+message is replaced with a letter a certain distance up or down the alphabet
+(called the 'shift length' or key).
 
+For example, a Caeser Cipher is applied to the message `"Cat"` with a shift
+length of `3` would return `"Fdx"`. Each letter in the cipher text (encrypted
+message) is 3 letters down the alphabet from the original letter.
+
+Learn more about the Caeser Cipher here:
 https://learncryptography.com/classical-encryption/caesar-cipher
 
+In this exercise, a message and key (between -25 and 25) will be passed in as
+the second and third arguments, respectively. Your program must return the
+cipher text.
+
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 ## HINTS
 
-Create a new file with a `.js` extension and start writing JavaScript! Make sure you're function is exported from the node module. Execute your program by running it with the `node` command. e.g.:
+Create a new file with a `.js` extension and start writing JavaScript! Make sure
+you're function is exported from the node module. Execute your program by
+running it with the `node` command. e.g.:
 
-```sh
-$ node program.js
-```
+```sh $ node program.js ```
 
 When you are done, you must run:
 
-```sh
-$ {appname} verify program.js
-```
+```sh $ {appname} verify program.js ```
 
-to proceed. Your program will be tested, a report will be generated, and the lesson will be marked 'completed' if you are successful.
+to proceed. Your program will be tested, a report will be generated, and the
+lesson will be marked 'completed' if you are successful.
 
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