Improve documentation for availability rules

[Valentina R]

Add examples of real-life availability rules and outcomes. Examples: * many people don't understand that a Range of Days/Months means 24 hours during those days/months, * they don't see that they can have the Availability set to YES or NOT * they don't understand the priority with the numbers and across global, product, staff)

[mattias @ refine.digital]

@Valentina - IMHO it doesn't solve the core problem - Managing complex Availability and a great UX is not supported without a new approach. Adding complex availability slows things down a lot. Do you think an approach like this (https://bitbucket.org/bookingwp/woocommerce-appointments/issues/386/add-option-to-bind-staff-availability) would be more intuitive for users & developers?

[Željan Topić]

Issue #481 was marked as a duplicate of this issue.

[Željan Topić]

Fixed from 4.4.0 onward