Add documentation about browserstack configuration (#490)

* Add some documentation on configurating BrowserStack

* Add link to browser support doc

README.md

@@ -95,7 +95,7 @@ Run Origami specification tests and component specific tests.
 Checks Sass supports [silent and non-silent compilation modes](http://origami.ft.com/docs/syntax/scss/#silent-styles).
 If `pa11y.html` demo exists, confirms it is accessible using [Pa11y](http://pa11y.org/).
 If `package.json` contains a `test` script, confirms it exits with a 0 exit code.
-Runs tests using [Karma](https://karma-runner.github.io) defaulting to Chrome Stable, can be configured to use BrowserStack by using the `--browserstack` flag.
+Runs tests using [Karma](https://karma-runner.github.io) defaulting to Chrome Stable, can be configured to use BrowserStack by using the `--browserstack` flag. You will need the environment variables `BROWSER_STACK_USERNAME` and `BROWSER_STACK_ACCESS_KEY` set. This will run the tests on the minimum version for enhanced experience based on the [FT Browser Support Policy[(https://docs.google.com/document/d/1mByh6sT8zI4XRyPKqWVsC2jUfXHZvhshS5SlHErWjXU).
 
 ## Migration guide
 

lib/origami-build-tools-cli.js

@@ -36,7 +36,7 @@ const help = `
 			--build-folder=<dir>       Compiled assets directory (default: ./build/)
 			-v, --version              Print out version of origami-build-tools
 			--production               Compiled assets will be minified for production systems
-			--browserstack             Run tests using Browserstack instead of Chrome Stable
+			--browserstack             Run tests using Browserstack instead of Chrome Stable. Requires BROWSER_STACK_USERNAME and BROWSER_STACK_ACCESS_KEY to be set.
 			--standalone               Create a named export for the built JavaScript
 
 		Full documentation