docs: add packages section to README.md (#503)

* docs: add packages section to README.md

* Update README.md

Author: 38elements

README.md

@@ -1,18 +1,19 @@
 # Vue Test Utils [![Build Status](https://circleci.com/gh/vuejs/vue-test-utils/tree/dev.png?style=shield)](https://circleci.com/gh/vuejs/vue-test-utils)
 
-## Currently in beta
-To use Vue Test Utils beta:
-```
-// npm
-npm install --save-dev @vue/test-utils
+## Packages
 
-// yarn
-yarn add --dev @vue/test-utils
-```
+This repository provides the following two packages.  
+They are currently in beta.
+
+* [Vue Test Utils](./packages/test-utils)
+* [Vue Server Test Utils](./packages/server-test-utils)
 
-## Intro
+You can install these packages by the following command.
 
-Vue Test Utils is the official test library for [Vue.js](http://vuejs.org). It provides methods for unit testing Vue components.
+```
+npm install --save-dev @vue/test-utils
+npm install --save-dev @vue/server-test-utils
+```
 
 ## Documentation