feat: add support for Gitpod workspaces

This change adds the configuration and documentation to use Gitpod 
(http://gitpod.io) workspaces that are setup with everything required to contribute to CDK.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

.gitpod.yml

@@ -0,0 +1,7 @@
+image: jsii/superchain
+tasks:
+  - init: yarn build --skip-test --no-bail
+
+vscode:
+  extensions:
+    - dbaeumer.vscode-eslint@2.1.5:9Wg0Glx/TwD8ElFBg+FKcQ==

CONTRIBUTING.md

@@ -47,7 +47,31 @@ and let us know if it's not up-to-date (even better, submit a PR with your  corr
 
 ## Getting Started
 
-For day-to-day development and normal contributions, the following SDKs and tools are required:
+### Gitpod
+
+For setting up a local development environment,
+we recommend using [Gitpod](http://gitpod.io) -
+a service that allows you to spin up an in-browser
+Visual Studio Code-compatible editor,
+with everything set up and ready to go for CDK development.
+Just click the button below to create your private workspace:
+
+[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/aws/aws-cdk)
+
+This will start a new Gitpod workspace,
+and immediately kick off a build of the CDK code.
+Once it's done (it takes around an hour, unfortunately),
+you can work on any package that you want to modify,
+as described in ['Quick Iteration'](#quick-iteration) below.
+
+Gitpod is free for 50 hours per month -
+make sure to stop your workspace when you're done
+(you can always resume it later, and it won't need to run the build again).
+
+### Local dependencies
+
+If you don't want to use Gitpod,
+you need to have the following SDKs and tools locally:
 
 - [Node.js >= 10.13.0](https://nodejs.org/download/release/latest-v10.x/)
   - We recommend using a version in [Active LTS](https://nodejs.org/en/about/releases/)

README.md

@@ -2,6 +2,7 @@
 
 ![Build Status](https://codebuild.us-east-1.amazonaws.com/badges?uuid=eyJlbmNyeXB0ZWREYXRhIjoiSy9rWmVENzRDbXBoVlhYaHBsNks4OGJDRXFtV1IySmhCVjJoaytDU2dtVWhhVys3NS9Odk5DbC9lR2JUTkRvSWlHSXZrNVhYQ3ZsaUJFY3o4OERQY1pnPSIsIml2UGFyYW1ldGVyU3BlYyI6IlB3ODEyRW9KdU0yaEp6NDkiLCJtYXRlcmlhbFNldFNlcmlhbCI6MX0%3D&branch=master)
 [![Gitter chat](https://badges.gitter.im/gitterHQ/gitter.svg)](https://gitter.im/awslabs/aws-cdk)
+[![Gitpod Ready-to-Code](https://img.shields.io/badge/Gitpod-ready--to--code-blue?logo=gitpod)](https://gitpod.io/#https://github.com/aws/aws-cdk)
 [![NPM version](https://badge.fury.io/js/aws-cdk.svg)](https://badge.fury.io/js/aws-cdk)
 [![PyPI version](https://badge.fury.io/py/aws-cdk.core.svg)](https://badge.fury.io/py/aws-cdk.core)
 [![NuGet version](https://badge.fury.io/nu/Amazon.CDK.svg)](https://badge.fury.io/nu/Amazon.CDK)