Merge pull request #1682 from yildiz/patch-1

Explained why it should not work in Chapter 4.1

src/variable_bindings/mut.md

@@ -15,9 +15,8 @@ fn main() {
 
     println!("After mutation: {}", mutable_binding);
 
-    // Error!
+    // Error! Cannot assign a new value to an immutable variable
     _immutable_binding += 1;
-    // FIXME ^ Comment out this line
 }
 ```