docs: add readme

packages/amplify-graphql-directives/Readme.md

@@ -0,0 +1,19 @@
+# Amplify GraphQL Directives
+
+Source of truth for the GraphQL directive definition used by the Amplify GraphQL API.
+
+> :warning: **Intended for internal Amplify use only.**
+
+## Description
+
+This package defines the GraphQL directives in GraphQL syntax.
+Each directive is imported into the corresponding GraphQL transformer.
+This package is responsible for the name, definition, and argument defaults for a directive.
+The GraphQL transformers utilize the GraphQL directives to define the behavior of the transform.
+
+This package also contains the AppSync GraphQL directives.
+These directives are defined internally by AppSync.
+The definitions here are copied from the internal definition.
+
+This package is intended to be the only source of truth for the GraphQL directive definitions used by the Amplify GraphQL API.
+This package should be imported in place of reproducing the definitions in other packages.