Scheduler cron not documented

The readme in HEAD has no information on the fact that scheduler runs on every Drupal cron by default, and more importantly nothing about the new /scheduler/cron that can be crontabbed independently for more granular scheduling without bogging down your site by scheduling Drupal cron for every minute.

Patch for README included. (I feel a little silly doing a patch file for a readme, but as this is my first time patching documentation, I figure better safe than sorry.)