Rate limit documentation corrected

We corrected our rate-limit documentation so it matches how the API actually enforces limits:

• Real limits per endpoint. The Rate Limiting page now lists the actual per-minute limit for every documented endpoint instead of example numbers. For example, ip-lookup and domain-lookup allow 100 requests per minute, and most other endpoints allow 60.
• Scope. Limits apply per account (all API keys of an account share them) and are counted separately per endpoint. They are not per API key or per IP address.
• Window. Limits use a fixed one-minute window. There are no daily or monthly request quotas; usage beyond that is governed by your credits.
• Reset header. X-RateLimit-Reset is a Unix timestamp marking when the window resets, not a number of seconds.

The Rate Limit Exceeded error page has been updated to match.