Readme: add a link to selenium docs
The new generation of php-webdriver.

Summary:

Test Plan:

Reviewers:

CC:

Task ID: #

Blame Rev:
Adding timeouts configuration

Change the timeout setting by:
$driver->manage()->timeouts()
  ->implicitlyWait(3)
  ->setScriptTimeout(5);
license header in WebDriverTimeouts and WebDriverOptions
Add the contributing section and the CLA link to README.md