Add more information to changesets

Author: kazekyo

.changeset/short-toes-relax.md

@@ -7,4 +7,64 @@
 "@graphql-codegen/graphql-modules-preset": minor
 ---
 
-Add a feature to transform documents
+Add a feature to transform documents.
+
+Plugin will have the following functions:
+```my-plugin.js
+module.exports = {
+  plugin: () => {
+    return 'hello'
+  },
+  transformDocuments: (_schema, documents) => {
+    // Make some changes to the documents
+    return documents;
+  },
+  validateBeforeTransformDocuments: () => {
+    // Raises an error if necessary
+  },
+};
+```
+
+Use it as follows:
+
+```ts
+import type { CodegenConfig } from '@graphql-codegen/cli'
+
+const config: CodegenConfig = {
+   schema: 'https://localhost:4000/graphql',
+   documents: ['src/**/*.tsx'],
+   generates: {
+      './src/gql/': {
+        preset: 'client',
+        documentTransformPlugins: ['./my-plugin.js'],
+        plugins: ['./my-plugin.js']
+      }
+   }
+}
+export default config
+```
+
+For example, to remove a `@localOnlyDirective` directive from documents:
+
+```my-plugin.js
+const { visit, print } = require('graphql')
+
+module.exports = {
+  plugin(schema, documents, config) {
+    // Output `documents` as an example.
+    return documents.map(documentFile => `${print(documentFile.document)}`).join('\n')
+  },
+  transformDocuments(schema, documents, config) {
+    return documents.map(documentFile => {
+      documentFile.document = visit(documentFile.document, {
+        Directive: {
+          leave(node) {
+            if (node.name.value === 'localOnlyDirective') return null
+          }
+        }
+      })
+      return documentFile
+    })
+  }
+}
+```