Update README.md

Added a branching explanation to the readme so that users can pick the right code to download
Fixing an issue, where session cookie is not found if Drupal is installed under base domain (example.com, without www) and Moodle in a subdomain (moodle.example.com). Assuming custom cookie domain is not used, Drupal does not hard code the leading dot in the session cookie hash, so Moodle should mirror that behavior.
Merge pull request #28 from pchec/master

Fix to session cookie mismatch in a specific domain setup
Get CSRF Token before login as well. Proves more reliable after the first attempt.
Additional error handling.
Merge pull request #33 from dmsmidt/master

Additional error handling / feedback + CSRF token get before login