Add document about overlaybd

Since nerdctl has been supported overlaybd in containerd#603 but missing document.
This pr adds the description in it.

Signed-off-by: Yifan Yuan <[email protected]>

Author: BigVan

README.md

@@ -13,7 +13,7 @@
 
  ✅ [Optional] Supports [rootless mode, without slirp overhead (bypass4netns)](./docs/rootless.md)
 
- ✅ [Optional] Supports lazy-pulling ([Stargz](./docs/stargz.md), [Nydus](./docs/nydus.md))
+ ✅ [Optional] Supports lazy-pulling ([Stargz](./docs/stargz.md), [Nydus](./docs/nydus.md), [OverlayBD](./docs/overlaybd.md))
 
  ✅ [Optional] Supports [encrypted images (ocicrypt)](./docs/ocicrypt.md)
 

docs/overlaybd.md

@@ -0,0 +1,29 @@
+# Lazy-pulling using OverlayBD Snapshotter
+
+| :zap: Requirement | nerdctl >= 0.15.0 |
+| ----------------- | --------------- |
+
+OverlayBD is a remote container image format base on block-device which is an open-source implementation of paper ["DADI: Block-Level Image Service for Agile and Elastic Application Deployment. USENIX ATC'20".](https://www.usenix.org/conference/atc20/presentation/li-huiba)
+
+See https://github.com/containerd/accelerated-container-image to learn further information.
+
+## Enable lazy-pulling for `nerdctl run`
+
+- Install containerd remote snapshotter plugin (`overlaybd`) from https://github.com/containerd/accelerated-container-image/blob/main/docs/BUILDING.md
+
+- Add the following to `/etc/containerd/config.toml`:
+```toml
+[proxy_plugins]
+  [proxy_plugins.overlaybd]
+    type = "snapshot"
+    address = "/run/overlaybd-snapshotter/overlaybd.sock"
+```
+
+- Launch `containerd` and `overlaybd-snapshotter`
+
+- Run `nerdctl` with `--snapshotter=overlaybd`
+```console
+nerdctl run --net host -it --rm --snapshotter=overlaybd registry.hub.docker.com/overlaybd/redis:6.2.1_obd
+```
+
+For more details about how to build overlaybd image, please refer to [accelerated-container-image](https://github.com/containerd/accelerated-container-image/blob/main/docs/IMAGE_CONVERTOR.md) conversion tool.