readme: used to_prepare instead of to_complete for tenant reset on console reload

[pragun16]

Issue Description: The QoL tip in the configuration option specifies the use of to_complete reloader callback to set ActsAsTenant.current_tenant which works fine during the console startup but does not reset the tenant on console reload.

Also referenced in this issue.

Proposed fix: to_complete does not seem to work well in a console environment and thus, replacing it with to_prepare resets the tenant correctly, although the callback runs twice on console reload!