Update Rate Limit Docs

[jamfish]

Howdy Devs,

Submitting this because I just had very long issue that could've been solved with documentation note, and I can't cut a PR for this.

Could it be updated so that https://github.com/terraform-providers/terraform-provider-cloudflare/blob/master/website/docs/r/rate_limit.html.markdown reflects:

• That there's set defaults for the 'period' argument (support noted 60, 3600, or 86400 seconds)
• The challenge and challenge_js modes for the action block (reflecting Allow zone_id to set zone and vice versa #174 EDIT: Add challenge and js_challenge rate-limit modes #172)?

Thanks,

Jam

[jacobbednarz]

* That there's set defaults for the 'period' argument (support noted 60, 3600, or 86400 seconds)

It's not this simple unfortunately. Different plans have different limits so the provider validation can only account one of them (which we've chosen as Enterprise as that is the outer limits of all). I don't know how we can better represent this in the documentation without doing something like this for all properties:

Valid values:

• Enterprise: 10
• Paid: 5
• Free: 1

* The `challenge` and `challenge_js` modes for the action block (reflecting #174)?

I think #174 is the wrong reference here as it's for zone/zone_id changes but updating the actions.mode documentation is 👍.

[jacobbednarz]

PR'd the changes the second bit in #293

[jamfish]

Thanks for this @jacobbednarz! Yeah, was totally wrong as I meant #171 and #172.