Add pattern\example for Stepper with validation

[ad9242]

💬 Description

Currently on the site there is some brief text for stepper validation. However there is no example of how this might be implemented and there have been questions from users as to how you could do this.

💰 Use value

An example (possibly under the "Patterns") would be very useful to users to show how this should be implemented. The example should show not proceeding to the next step until validation errors have been resolved

[ad9242]

an image on the stepper guidance would be good too