Add changelog entry

CHANGELOG.md

@@ -1,4 +1,23 @@
 # Changelog
+
+## Unreleased
+- Add schema validation: Input Objects must not contain non-nullable circular references (https://github.com/webonyx/graphql-php/pull/492)
+
+#### v0.13.4
+- Force int when setting max query depth (https://github.com/webonyx/graphql-php/pull/477)
+
+#### v0.13.3
+- Reverted minor possible breaking change (https://github.com/webonyx/graphql-php/pull/476)
+
+#### v0.13.2
+- Added QueryPlan support (https://github.com/webonyx/graphql-php/pull/436)
+- Fixed an issue with NodeList iteration over missing keys (https://github.com/webonyx/graphql-php/pull/475)
+
+#### v0.13.1
+- Better validation of field/directive arguments
+- Support for Apollo-style client/server persisted queries
+- Minor tweaks and fixes
+
 ## v0.13.0
 This release brings several breaking changes. Please refer to [UPGRADE](UPGRADE.md) document for details.
 

CONTRIBUTING.md

@@ -10,8 +10,9 @@ For smaller contributions just use this workflow:
 * Fork the project.
 * Add your features and or bug fixes.
 * Add tests. Tests are important for us.
-* Check your changes using `composer check-all`
-* Send a pull request
+* Check your changes using `composer check-all`.
+* Add an entry to the [Changelog](CHANGELOG.md).
+* Send a pull request.
 
 ## Setup the Development Environment
 First, copy the URL of your fork and `git clone` it to your local machine.