specify the syntax highlight to code snippet in error doc
@@ -316,7 +316,7 @@ struct DebugError {
Now let's implement `ParseError` and `ContextError` on it:
-```
+```rust
impl ParseError<&str> for DebugError {
// on one line, we show the error code and the input that caused it
fn from_error_kind(input: &str, kind: ErrorKind) -> Self {
