Add details for installation and usage in README

Author: fredericbarthelet

README.md

@@ -2,6 +2,51 @@
 
 Typescript definitions for Serverless service file.
 
+## Installation
+
+```
+npm i @serverless/typescript --save-dev
+```
+
+or
+
+```
+yarn add @serverless/typescript --dev
+```
+
+## Usage
+
+`serverless.ts` file
+
+```ts
+import type { AWS } from '@serverless/typescript';
+
+const serverlessConfiguration: AWS = {
+  service: 'aws-nodejs-typescript',
+  },
+  frameworkVersion: '*',
+  provider: {
+    name: 'aws',
+    runtime: 'nodejs12.x',
+  },
+  functions: {
+    hello: {
+      handler: 'handler.hello',
+      events: [
+        {
+          http: {
+            method: 'get',
+            path: 'hello',
+          }
+        }
+      ]
+    }
+  }
+}
+
+module.exports = serverlessConfiguration;
+```
+
 ## Remaining improvements
 
 ### Use Record<> instead