Update example of :verify_authorized
Update example of :verify_authorized

## Why is this change necessary?

- Make the example more newbie friendly.
- I saw one of my colleague copied and pasted this code snippet but
didn’t notice that the verification for index was totally off.
- Official README is widely trusted. It will be great if we can make it
more newbie friendly.

## How does it address the issue?

- Remove `except` option from `verify_authorized` example.
- Add `before_action :verify_authorized` to `verify_policy_scoped`
example to complete a scenario.

yatmsu/pundit,maxcal/pundit,elabs/pundit