add serializer file

packages/jest-emotion/README.md

@@ -10,7 +10,19 @@ npm install --save-dev jest-emotion
 
 # Snapshot Serializer
 
-The easiest way to test React components with emotion is with the snapshot serializer. (the example below is with react-test-renderer but jest-emotion also works with enzyme)
+The easiest way to test React components with emotion is with the snapshot serializer. You can register the serializer via the `snapshotSerializers` configuration property in your jest configuration like so:
+
+```js
+// jest.config.js
+module.exports = {
+  // ... other config
+  snapshotSerializers: [
+    'jest-emotion/serializer'
+  ]
+}
+```
+
+Or you can customize the serializer via the `createSerializer` method like so: (the example below is with react-test-renderer but jest-emotion also works with enzyme and react-testing-library)
 
 ```jsx
 import React from 'react'

packages/jest-emotion/package.json

@@ -7,7 +7,8 @@
   "files": [
     "src",
     "dist",
-    "types"
+    "types",
+    "serializer.js"
   ],
   "scripts": {
     "test:typescript": "dtslint types"

packages/jest-emotion/serializer.js

@@ -0,0 +1,4 @@
+const { createSerializer } = require('jest-emotion')
+const emotion = require('emotion')
+
+module.exports = createSerializer(emotion)