Add Loader.io example

[stevector]

I have used Loader.io in Quicksilver demos and should bring over my code to this repo. It also includes some Slack reporting.

The purpose of the script is to trigger a load test of Test or Live upon deployment.

[stevector]

I'm currently having trouble testing my script on a fresh install because of https://github.com/pantheon-systems/terminus-secrets-plugin/issues/10