Specify format of kubernetes.namespaces (#894)

Signed-off-by: Dan Barr <6922515+danbarr@users.noreply.github.com>

Author: danbarr

docs/toolhive/guides-registry/configuration.mdx

@@ -395,9 +395,10 @@ registries:
 **Configuration options:**
 
 - `kubernetes` (required): Empty object or namespace configuration (see below)
-- `kubernetes.namespaces` (optional): List of Kubernetes namespaces to watch. If
-  empty, falls back to the `THV_REGISTRY_WATCH_NAMESPACE` environment variable,
-  or all namespaces if neither is set
+- `kubernetes.namespaces` (optional): A comma-separated list of Kubernetes
+  namespaces to watch. If empty, falls back to the
+  `THV_REGISTRY_WATCH_NAMESPACE` environment variable, or all namespaces if
+  neither is set
 - No sync policy required (Kubernetes sources query live deployments on-demand)
 
 #### Per-entry claims via annotation