Adding Tester Docs + Removing the old Compiler (#691)

* update readme

* remove the legacy compiler

* readme tweak

Author: pooyaj

README.md

@@ -34,7 +34,15 @@ If you need to add an external dependency to an integration, **please ensure you
 Each integration directory has an npm script called `test` that you can use to easily run the unit tests with via `yarn test`.
 
 ### Test Locally
-You can test changes to integrations locally with the [a.js compiler](https://github.com/segmentio/analytics.js-integrations/tree/master/compiler).
+To test changes locally you can run: 
+
+```
+yarn --cwd tester install
+yarn dev
+```
+This will open the local development environment. To test a particular destination, enter a writeKey that has the destination connected, and the tool will load Analytics.js with the local version of the destinations connected, and the settings for the source. After the first load, you can referesh the page without having to load the writeKey each time. 
+
+If you want to test a new destination or a new settings parameter, you can override the settings using the integrated JSON editor. To fire track, page, etc. calls, you can use the Chrome DevTools and fire events using `analytics.track( .... )` etc. 
 
 ### Code Formatting
 This project uses eslint to ensure uniform code formatting standards are maintained. You can see the specific eslint config in the root `.eslintrc` file. A pre-commit hook is used to help automate this process for you.