docs: add mode=max to in-cluster building docs

docs/guides/in-cluster-building.md

@@ -170,6 +170,50 @@ effect: "NoSchedule"
 
 This allows you to set corresponding [Taints](https://kubernetes.io/docs/concepts/scheduling-eviction/taint-and-toleration/) on cluster nodes to control which nodes builder deployments are deployed to. You can also configure a [`nodeSelector`](../reference/providers/kubernetes.md#providersclusterbuildkitnodeselector) to serve the same purpose.
 
+#### Caching
+
+By default, cluster-buildkit will have two layers of cache
+
+1. A local file cache, maintained by the cluster-buildkit instance. The cache is shared for all builds in the same namespace
+2. A `_buildcache` image tag in the configured deploymentRegistry will be used as an external cache. This is useful for fresh namespaces, e.g. preview environments
+
+You can customize the cache configuration with the `cache` option. You can list multiple cache layers, and it will choose the first one that generates any hit for all following layers.
+
+In a large team it might be beneficial to use a more complicated cache strategy, for example the following:
+
+```yaml
+clusterBuildkit:
+  cache:
+      - type: registry
+        tag: _buildcache-${slice(kebabCase(git.branch), "0", "30")}
+      - type: registry
+        tag: _buildcache-main
+        export: false
+```
+
+With this configuration, every new feature branch will benefit from the main branch cache, while not polluting the main branch cache (via `export: false`).
+Any subsequent builds will use the feature branch cache.
+
+Please keep in mind that you should also configure a garbage collection policy in your Docker registry to clean old feature branch tags.
+
+#### Multi-stage caching
+
+If your `Dockerfile` has multiple stages, you can benefit from `mode=max` caching. It is automatically enabled, if your registry is not in our list of unsupported registries.
+Currently, those are AWS ECR and Google GCR. If you are using GCR, you can switch to the Google Artifact Registry, which supports `mode=max`.
+
+You can also configure a different cache registry for your images. That way you can keep using ECR or GCR, while having better cache hit rate with `mode=max`:
+
+```yaml
+clusterBuildkit:
+  cache:
+      - type: registry
+        registry:
+          hostname: hub.docker.com
+          namespace: my-team-cache
+```
+
+For this mode of operation you need secrets for all the registries configured in your `imagePullSecrets`.
+
 ### cluster-docker
 
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