docs: add cache persistence notes for docker-container driver

Signed-off-by: Justin Chadwell <me@jedevc.com>

docs/manuals/drivers/docker-container.md

@@ -78,7 +78,42 @@ REPOSITORY                       TAG               IMAGE ID       CREATED
 <image>                          latest            adf3eec768a1   2 minutes ago       197MB
 ```
 
-### QEMU
+## Cache persistence
+
+The `docker-container` driver supports cache persistence, as it stores all of
+the BuildKit state and related cache into a dedicated docker volume.
+
+To persist the `docker-container` driver's cache, even after recreating the
+driver using `docker buildx rm` and `docker buildx create`, you can destroy the
+builder using the `--keep-state` flag:
+
+For example, to create a builder named `container` and then remove it while
+persisting state:
+
+```console
+# setup a builder
+$ docker buildx create --name=container --driver=docker-container --use --bootstrap
+container
+$ docker buildx ls
+NAME/NODE       DRIVER/ENDPOINT              STATUS   BUILDKIT PLATFORMS
+container *     docker-container                               
+  container0    desktop-linux                running  v0.10.5  linux/amd64
+$ docker volume ls
+DRIVER    VOLUME NAME
+local     buildx_buildkit_container0_state
+
+# remove the builder while persisting state
+$ docker buildx rm --keep-state container
+$ docker volume ls
+DRIVER    VOLUME NAME
+local     buildx_buildkit_container0_state
+
+# the newly created driver with the same name will have all the state of the previous one!
+$ docker buildx create --name=container --driver=docker-container --use --bootstrap
+container
+```
+
+## QEMU
 
 The `docker-container` driver supports using [QEMU](https://www.qemu.org/) (user
 mode) to build non-native platforms. Use the `--platform` flag to specify which