Mention requiring the gem in the README
Mention requiring the gem in the README

I'm seeing this error:

    unable to connect to chromedriver 127.0.0.1:9515
      (Selenium::WebDriver::Error::WebDriverError)

PR #58 changes the "chromedriver" executable file name to
"chromedriver-helper", but I found that
Selenium::WebDriver::Chrome.driver_path was nil after trying to visit a
page (after rescuing from the failure).

The problem is that I was never loading the new chromedriver-helper code
to set the custom driver_path.  I added this to features/support/env.rb
and my Cucumber scenario started working:

    require "chromedriver-helper"

I'm using this outside of Rails in a standalone test suite to test an
app that is developed separately.  (Rails may be requiring the gem
behind the scenes.)

Mention the possible need to require "chromedriver-helper" in the
Standalone section of the README, where people will be looking for
installation instructions.

flavorjones/chromedriver-helper,flavorjones/chromedriver-helper,flavorjones/chromedriver-helper