Add documentation for Scoped HRQs in user guide (#25)

- Introduced a section on using Scoped HRQs, detailing their purpose and functionality.
- Included an example YAML configuration for creating a scoped HRQ.
- Clarified the use of the `scopeSelector` field in relation to Kubernetes ResourceQuota.

This enhances resource management strategies within namespace hierarchies.

Author: ryotarai

docs/user-guide/how-to.md

@@ -202,6 +202,34 @@ teams, and those teams can distribute their resources between their subteams.
 
 Note: Decimal point values cannot be specified in HRQ (you can't do `cpu: 1.5` but you can do `cpu: "1.5"` or `cpu: 1500m`). See [#292](https://github.com/kubernetes-sigs/hierarchical-namespaces/issues/292)
 
+#### Using Scoped HRQs
+
+In addition to regular HRQs that apply to all resources, you can create **scoped HRQs** that only apply to resources matching specific criteria. This enables more sophisticated resource management strategies within a single namespace hierarchy.
+
+- Multiple scoped HRQs can exist in the same namespace hierarchy
+- Each scoped HRQ operates independently and only affects matching resources
+
+**Creating a scoped HRQ:**
+
+```yaml
+apiVersion: hnc.x-k8s.io/v1alpha2
+kind: HierarchicalResourceQuota
+metadata:
+  name: production-workloads
+  namespace: team-namespace
+spec:
+  hard:
+    cpu: "20"
+    memory: "40Gi"
+  scopeSelector:
+    matchExpressions:
+    - operator: In
+      scopeName: PriorityClass
+      values: ["production"]
+```
+
+The `scopeSelector` field works exactly like the standard Kubernetes ResourceQuota `scopeSelector`. For details on available scopes and configuration options, see the [Kubernetes ResourceQuota documentation](https://kubernetes.io/docs/concepts/policy/resource-quotas/#quota-scopes).
+
 <a name="use-select"/>
 
 ### Select namespaces based on their hierarchies
@@ -980,4 +1008,4 @@ Interesting parameters include:
   exclude an object from propagation.
     * Rancher objects that have the label `cattle.io/creator=norman` are not propagated
     by the default manifests (refer to [Concepts: built in exceptions](concepts.md#built-in-exceptions)
-    for more information).
+    for more information).