Explain what's the behavior of valid redirect rules

[calavera]

- Do you want to request a feature or report a bug?

This is a feature.

- What is the current behavior?

When redirect rules are valid, we only say that they are valid.

- What is the expected behavior?

We should explain each rule and what the effect of a match in the rule will have. For example:

/foo https://foo.com/bar 301!
=> Requests to the path /foo will be redirected to https://foo.com/bar.
=> The redirect will happen regardless the site can serve content in /foo or not,
=> because the redirect is using `!`.

[whmountains]

I came here to ask for this feature too!

[scottlet]

This! Also, it would be amazing to be able to paste in a rule and see what it hits - debugging this feature is a pain.