Update CHANGELOG & Docs

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.9.0] 2021-06-01
+
+- Add support for returning multiple resolver errors. [#531](https://github.com/async-graphql/async-graphql/issues/531)
+
+- Bump upstream crate `multer` from `v1.2.2` to `v2.0.0`. 
+
 ## [2.8.6] 2021-06-01
 
 - Allow the ability to set GraphQL Playground settings. [#508](https://github.com/async-graphql/async-graphql/pull/508)

src/context.rs

@@ -281,7 +281,9 @@ impl<'a, T> ContextBase<'a, T> {
         }
     }
 
-    #[doc(hidden)]
+    /// Report a resolver error.
+    ///
+    /// When implementing `OutputType`, if an error occurs, call this function to report this error and return `Value::Null`.
     pub fn add_error(&self, error: ServerError) {
         match self.path_node {
             Some(node) => {