Add example of using guards with case expression (documentationjs#339)

* Add example of using guards with case expression

* Apply review feedback

Author: milesfrain

language/Pattern-Matching.md

@@ -176,6 +176,29 @@ compare _ _ = EQ
 
 (The name `otherwise` is a synonym for `true` commonly used in guards.)
 
+Guards may also be used within `case` expressions, which allow for inline expressions. For example, these are equivalent: 
+
+```purs
+fb :: Int -> Effect Unit
+fb = log <<< case _ of
+  n
+    | 0 == mod n 15 -> "FizzBuzz"
+    | 0 == mod n 3 -> "Fizz"
+    | 0 == mod n 5 -> "Buzz"
+    | otherwise -> show n
+```
+
+```purs
+fb :: Int -> Effect Unit
+fb n = log x
+  where
+  x
+    | 0 == mod n 15 = "FizzBuzz"
+    | 0 == mod n 3 = "Fizz"
+    | 0 == mod n 5 = "Buzz"
+    | otherwise = show n
+```
+
 Pattern Guards
 --------------