Add a basic DEVELOPMENT file to explain common scenarios (#475)

* Add a basic DEVELOPMENT file to explain common scenarios

* Add environment info to development file

DEVELOPMENT.md

@@ -0,0 +1,53 @@
+## Environment
+
+- Node >= 10.x
+
+## Building
+
+The SDK uses [Rollup](https://rollupjs.org/guide/en/) to compile all JavaScript assets into a set of output modules to be consumed by other module builders such as [Webpack](https://webpack.js.org/) and Rollup, or directly into and HTML file via the CDN.
+
+To perform a build, use the `build` script:
+
+```
+npm run build
+```
+
+## Running Tests
+
+### Unit tests
+
+Unit tests can be executed using [Jest](https://jestjs.io/) by issuing the following command:
+
+```
+npm test
+```
+
+To interactively perform tests using Jest's `watch` mode, use:
+
+```
+npm run test:watch
+```
+
+### Integration tests
+
+Integration tests can be run through [Cypress](https://www.cypress.io/) to perform integration testing using the SDK and Auth0. To run these, use:
+
+```
+npm run test:integration
+```
+
+To perform these tests interactively and watch the output, use:
+
+```
+npm run test:watch:integration
+```
+
+## The SDK Playground
+
+To test the SDK manually and play around with the various options and features, you can invoke the Playground by using:
+
+```
+npm start
+```
+
+This will open a web server on `http://localhost:3000` and display a simple web app that allows you to manually perform various features of the SDK. This is preconfigured with an Auth0 tenant and client ID but you may change this to your own for testing.