Docs: make it very obvious that Heroku Scheduler is "best effort", not guarenteed

[ghost]

The Heroku Scheduler add-on is the suggested method for triggering bot runs (iterations where votes are cast) as described in the installation instructions.

It should be very clearly noted that it is a "best effort" service and may not run every time it is supposed to.

From their manual page:

Scheduler is a “best effort” service, meaning that execution is expected but not guaranteed. Scheduler is known to occasionally (but rarely) miss the execution of scheduled jobs. If scheduled jobs are a critical component of your application, it is recommended to run a custom clock process instead for more reliability, control, and visibility.

This is important information and do avoid confusion and disappointment it should be clear in the instructions.

[ghost]

Fixed for v0.2.10