Adds comma

Oddly (to me), this code runs fine without the comma separating the `Some` and `None` arms of the `match` construct. It seems like Rust doesn't require you to separate arms with commas if all the expressions are enclosed in braces.

Author: O-I

src/doc/guide.md

@@ -4209,7 +4209,7 @@ loop {
     match range.next() {
         Some(x) => {
             println!("{}", x);
-        }
+        },
         None => { break }
     }
 }