Update system-requirements.md - kURL Firewall Openings (#962)

I just did a test kURL installation, and found we're pulling the packages down from s3.kurl.sh also. We should reference this on the list of domains for people adding firewall/proxy exceptions etc.

picked up as part of replicated-collab/bigid-kots#149 (comment)

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thanks to @jonquil2002 for noticing I need to update this here also - ref replicatedhq/replicated-docs#1089 (comment) :)

src/markdown-pages/install-with-kurl/system-requirements.md

@@ -120,7 +120,7 @@ IP addresses for these services can be found in [replicatedhq/ips](https://githu
 |---------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | amazonaws.com | tar.gz packages are downloaded from Amazon S3 during embedded cluster installations. The IP ranges to allowlist for accessing these can be scraped dynamically from the [AWS IP Address](https://docs.aws.amazon.com/general/latest/gr/aws-ip-ranges.html#aws-ip-download) Ranges documentation. |
 | k8s.gcr.io, registry.k8s.io | Images for the Kubernetes control plane are downloaded from the [Google Container Registry](https://cloud.google.com/container-registry) repository used to publish official container images for Kubernetes. Starting March 20, 2023, these requests are proxied to the new address `registry.k8s.io`. Both of these URLs must be allowed network traffic using firewall rules. For more information on the Kubernetes control plane components, see the [Kubernetes documentation](https://kubernetes.io/docs/concepts/overview/components/#control-plane-components). |
-| k8s.kurl.sh   | Kubernetes cluster installation scripts and artifacts are served from [kurl.sh](https://kurl.sh). Bash scripts and binary executables are served from kurl.sh. This domain is owned by Replicated, Inc which is headquartered in Los Angeles, CA. |
+| k8s.kurl.sh, s3.kurl.sh   | Kubernetes cluster installation scripts and artifacts are served from [kurl.sh](https://kurl.sh). Bash scripts and binary executables are served from kurl.sh. This domain is owned by Replicated, Inc which is headquartered in Los Angeles, CA. |
 
 No outbound internet access is required for airgapped installations.
 ### Host Firewall Rules