Make auto-generated emails customisable

Currently the auto-generated emails are fairly threadbare with information. I'd like the email content to be customisable, for example:
- I could customise the auto-generated "New User" email to provide links to navigation tutorials plus links to registration for formal training.
- I could also customise the dashboard emails with "What do I do here?" links to detailed explanations of their requirements.
I'm sure others would find this useful for their own bespoke needs.