[16.0][IMP] mail_post_defer: Add notes to readme

[nobuQuartile]

We encounter an issue where scheduled messages are not sent because the cron job "Notification: Send scheduled message notifications" (mail.ir_cron_send_scheduled_message) is inactive.

The cron record is triggered here: https://github.com/OCA/OCB/blob/16.0/addons/mail/models/mail_message_schedule.py#L39

and it's ignored if not active: https://github.com/OCA/OCB/blob/16.0/odoo/addons/base/models/ir_cron.py#L486C9-L492C67

@qrtl QT4601

[OCA-git-bot]

Hi @Yajo, some modules you are maintaining are being modified, check this out!

[nobuQuartile]

I rebased the branch.

[yajo]

/ocabot merge patch

[yostashiro]

@yajo Perhaps approve the PR first, then try merging it again?

[OCA-git-bot]

On my way to merge this fine PR! Prepared branch 16.0-ocabot-merge-pr-1616-by-yajo-bump-patch, awaiting test results.

[OCA-git-bot]

Congratulations, your PR was merged at 9d2c8302831342c679579a21938ab552422f5293. Thanks a lot for contributing to OCA. ❤️