Add usage examples for integrating with browserstack and saucelabs

[arschmitz]

These are both very popular cross browser testing services so it would make sense to have examples showing their usage.

[dylanb]

@dsturley what was your experience using saucelabs and how much would it take to get this working with sauce?

@arschmitz it would be great if you could help us create a browserstack example

[dsturley]

Sauce at its heart is just a Selenium Server; adapted an integration test:

var WebDriver = require('selenium-webdriver'),
    assert = require('chai').assert,
    AxeBuilder = require('axe-webdriverjs');

describe('sauce-example', function () {
    this.timeout(10000);

    var driver;
    var url = 'https://github.com/dequelabs/axe-webdriverjs';
    before(function (done) {
        driver = new WebDriver.Builder()
            .usingServer('http://ondemand.saucelabs.com:80/wd/hub')
            .withCapabilities({
                browserName: 'Firefox',
                // you must set these environment variables
                username: process.env.SAUCE_USERNAME,
                accessKey: process.env.SAUCE_ACCESS_KEY
            })
            .build();

        driver
            .get(url)
            .then(function () {
                done();
            });
    });

    after(function () {
        driver.quit();
    });

    it('should find violations', function (done) {
        AxeBuilder(driver)
            .analyze(function (results) {
                assert.equal(results.url, url);
                done();
            });
    });

});

[arschmitz]

@dsturley browser stack works exactly the same.

My suggestion was simply to add examples like the one you have here to the documentation