Docs: Link to SDK Service Account (#3565)

"GameServer Pod Service Accounts" didn't provide a reference to what the
SDK service account permissions should be - so this updates the docs to
the point to the relevant Helm yaml file that is the reference for this,
with an accompanying warning on what getting your RBAC permissions
wrong can do.

Closes #3564

site/content/en/docs/Advanced/service-accounts.md

@@ -23,6 +23,14 @@ of the Kubernetes API.
 
 If needed, you can provide your own service account on the `Pod` specification in the `GameServer` configuration.
 
+{{< alert title="Warning" color="warning" >}}
+If you bring your own Service Account, it's your responsibility to ensure it matches all the RBAC permissions
+the `GameServer` `Pod` usually acquires from Agones by default, otherwise `GameServers` can fail.
+
+The default RBAC permissions for can be found in the {{< ghlink href="install/helm/agones/templates/serviceaccounts/sdk.yaml" >}}installation
+YAML on GitHub{{< /ghlink >}} and can be used for a reference.
+{{</ alert >}}
+
 For example:
 
 ```yaml