Clean up E0277 and E0282 explanations

src/librustc_error_codes/error_codes/E0277.md

@@ -1,5 +1,7 @@
 You tried to use a type which doesn't implement some trait in a place which
-expected that trait. Erroneous code example:
+expected that trait.
+
+Erroneous code example:
 
 ```compile_fail,E0277
 // here we declare the Foo trait with a bar method

src/librustc_error_codes/error_codes/E0282.md

@@ -1,3 +1,11 @@
+The compiler could not infer a type and asked for a type annotation.
+
+Erroneous code example:
+
+```compile_fail,E0282
+let x = "hello".chars().rev().collect();
+```
+
 This error indicates that type inference did not result in one unique possible
 type, and extra information is required. In most cases this can be provided
 by adding a type annotation. Sometimes you need to specify a generic type
@@ -8,13 +16,9 @@ parameter with a `FromIterator` bound, which for a `char` iterator is
 implemented by `Vec` and `String` among others. Consider the following snippet
 that reverses the characters of a string:
 
-```compile_fail,E0282
-let x = "hello".chars().rev().collect();
-```
-
-In this case, the compiler cannot infer what the type of `x` should be:
-`Vec<char>` and `String` are both suitable candidates. To specify which type to
-use, you can use a type annotation on `x`:
+In the first code example, the compiler cannot infer what the type of `x` should
+be: `Vec<char>` and `String` are both suitable candidates. To specify which type
+to use, you can use a type annotation on `x`:
 
 ```
 let x: Vec<char> = "hello".chars().rev().collect();