doc: Add documentation about client-generator-nextjs

Author: Gregcop1

client-generator/images/nextjs/client-generator-nextjs-list.png

@@ -10,6 +10,7 @@ It is able to generate apps using the following frontend stacks:
 
 * [React with Redux](react.md)
 * [React Native](react-native.md)
+* [Next.js](nextjs.md)
 * [Vue.js](vuejs.md)
 
 Client Generator works especially well with APIs built with the [API Platform](https://api-platform.com) framework.

client-generator/images/nextjs/client-generator-nextjs-show.png

@@ -0,0 +1,102 @@
+# Next.js Generator
+
+![List screenshot](images/nextjs/client-generator-nextjs-list.png)
+
+The Next.js Client Generator generates routes and components for Server Side Rendered applications using [Next.js](https://zeit.co/blog/next)
+
+## Install
+
+### Next + Express server
+
+Create a [Next.js application with express server](https://github.com/zeit/next.js/tree/canary/examples/custom-server-express). The easiest way is to execute:  
+
+```bash
+$ npx create-next-app --example custom-server-express your-app-name
+# or
+$ yarn create next-app --example custom-server-express your-app-name
+```
+
+### Enable Typescript
+
+Install typescript dependencies  
+
+```bash
+$ yarn add @types/next @zeit/next-typescript
+```
+
+Enable Typescript in your Next.js configuration file ("next.config.js")
+```javascript
+const withTypescript = require('@zeit/next-typescript');
+
+module.exports = withTypescript();
+```
+
+Create a ".babelrc" file to store Babel configuration
+```json
+{
+  "presets": [
+    "next/babel",
+    "@zeit/next-typescript/babel"
+  ]
+}
+```
+
+Create a "tsconfig.json" file to store Typescript configuration
+```json
+{
+  "compilerOptions": {
+    "allowJs": true,
+    "allowSyntheticDefaultImports": true,
+    "jsx": "preserve",
+    "lib": ["dom", "es2017"],
+    "module": "esnext",
+    "moduleResolution": "node",
+    "noEmit": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "preserveConstEnums": true,
+    "removeComments": false,
+    "skipLibCheck": true,
+    "sourceMap": true,
+    "strict": true,
+    "target": "esnext",
+    "typeRoots": [
+      "node_modules/@types"
+    ]
+  }
+}
+```
+
+### Generator dependencies
+
+Install required dependencies:
+
+```bash
+$ yarn add lodash @types/lodash isomorphic-unfetch
+```
+
+## Launch
+
+You can launch the server with 
+```bash
+$ yarn dev
+```
+
+and access it through [http://localhost:3000](http://localhost:3000)
+
+## Generating routes
+
+```bash
+$ npx @api-platform/client-generator https://demo.api-platform.com src/ -g next --resource book
+# Replace the URL by the entrypoint of your Hydra-enabled API
+```
+
+> Note: Omit the resource flag to generate files for all resource types exposed by the API.
+
+Go to `https://localhost:3000/books/` to start using your app.
+That's it!
+
+## Screenshots
+
+![List](images/nextjs/client-generator-nextjs-list.png)  
+![Show](images/nextjs/client-generator-nextjs-show.png)