add kubectl config set context namespace note

active/kubernetes/kubernetes.md

@@ -11,3 +11,10 @@ helm: <https://helm.sh/docs/intro/install/>
 For k3s, see [k3s](/active/software_k3s/k3s.md)
 
 For k0s, see [k0s](/active/software_k0s/k0s.md)
+
+## Notes
+
+```bash
+# Quickly set a new namespace
+kubectl config set contexts.default.namespace metallb-system
+```