clean up E0506 explanation

src/librustc_error_codes/error_codes/E0506.md

@@ -1,4 +1,4 @@
-This error occurs when an attempt is made to assign to a borrowed value.
+An attempt was made to assign to a borrowed value.
 
 Erroneous code example:
 
@@ -7,14 +7,12 @@ struct FancyNum {
     num: u8,
 }
 
-fn main() {
-    let mut fancy_num = FancyNum { num: 5 };
-    let fancy_ref = &fancy_num;
-    fancy_num = FancyNum { num: 6 };
-    // error: cannot assign to `fancy_num` because it is borrowed
+let mut fancy_num = FancyNum { num: 5 };
+let fancy_ref = &fancy_num;
+fancy_num = FancyNum { num: 6 };
+// error: cannot assign to `fancy_num` because it is borrowed
 
-    println!("Num: {}, Ref: {}", fancy_num.num, fancy_ref.num);
-}
+println!("Num: {}, Ref: {}", fancy_num.num, fancy_ref.num);
 ```
 
 Because `fancy_ref` still holds a reference to `fancy_num`, `fancy_num` can't
@@ -27,13 +25,11 @@ struct FancyNum {
     num: u8,
 }
 
-fn main() {
-    let mut fancy_num = FancyNum { num: 5 };
-    let moved_num = fancy_num;
-    fancy_num = FancyNum { num: 6 };
+let mut fancy_num = FancyNum { num: 5 };
+let moved_num = fancy_num;
+fancy_num = FancyNum { num: 6 };
 
-    println!("Num: {}, Moved num: {}", fancy_num.num, moved_num.num);
-}
+println!("Num: {}, Moved num: {}", fancy_num.num, moved_num.num);
 ```
 
 If the value has to be borrowed, try limiting the lifetime of the borrow using
@@ -44,18 +40,16 @@ struct FancyNum {
     num: u8,
 }
 
-fn main() {
-    let mut fancy_num = FancyNum { num: 5 };
-
-    {
-        let fancy_ref = &fancy_num;
-        println!("Ref: {}", fancy_ref.num);
-    }
+let mut fancy_num = FancyNum { num: 5 };
 
-    // Works because `fancy_ref` is no longer in scope
-    fancy_num = FancyNum { num: 6 };
-    println!("Num: {}", fancy_num.num);
+{
+    let fancy_ref = &fancy_num;
+    println!("Ref: {}", fancy_ref.num);
 }
+
+// Works because `fancy_ref` is no longer in scope
+fancy_num = FancyNum { num: 6 };
+println!("Num: {}", fancy_num.num);
 ```
 
 Or by moving the reference into a function:
@@ -65,17 +59,15 @@ struct FancyNum {
     num: u8,
 }
 
-fn main() {
-    let mut fancy_num = FancyNum { num: 5 };
-
-    print_fancy_ref(&fancy_num);
-
-    // Works because function borrow has ended
-    fancy_num = FancyNum { num: 6 };
-    println!("Num: {}", fancy_num.num);
-}
-
 fn print_fancy_ref(fancy_ref: &FancyNum){
     println!("Ref: {}", fancy_ref.num);
 }
+
+let mut fancy_num = FancyNum { num: 5 };
+
+print_fancy_ref(&fancy_num);
+
+// Works because function borrow has ended
+fancy_num = FancyNum { num: 6 };
+println!("Num: {}", fancy_num.num);
 ```