docs: clarify which error is returned by Response::mime()

src/client/response.rs

@@ -67,7 +67,8 @@ impl Response {
     }
 
     /// Get the response body MIME type by parsing the metadata field.
-    /// If you call this method on a non-2x response, you'll get a parse error.
+    /// If you call this method on a non-2x response, you'll get a parse error
+    /// ([`LibError::InvalidMime`]).
     /// It's strongly recommended to check the status code first
     /// (most handy is [`Response::is_ok()`]).
     pub fn mime(&self) -> Result<mime::Mime, LibError> {