docs(SentenceSmash): add question readme.

CodeWarsChallenges/CodeWarsChallenges/Strings/8kyu/Sentence Smash/SentenceSmash_Question.md

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+Sentence Smash
+Write a function that takes an array of words and smashes them together into a sentence and returns the sentence. You can ignore any need to sanitize words or add punctuation, but you should add spaces between each word. Be careful, there shouldn't be a space at the beginning or the end of the sentence!
+
+Example
+````csharp
+['hello', 'world', 'this', 'is', 'great']  =>  'hello world this is great'
+````
+
+``STRINGS ARRAYS FUNDAMENTALS``