clarify flattening single mac call

Author: calebcartwright

guide/expressions.md

@@ -661,7 +661,7 @@ match foo {
 ```
 
 If the body is a single expression with no line comments and not a control flow
-expression, then it may be started on the same line as the right-hand side. If
+expression nor a macro call expression, then it may be started on the same line as the right-hand side. If
 not, then it must be in a block. Example,
 
 ```rust
@@ -681,6 +681,9 @@ match foo {
             another_argument,
         )
     }
+    baz => {
+        macro_call!()
+    }
 }
 ```