add logo for overlaybd

Signed-off-by: liulanzheng <lanzheng.liulz@alibaba-inc.com>

README.md

@@ -1,6 +1,8 @@
 # Overlaybd
 
-Overlaybd is a novel layering block-level image format, which is design for container, secure container and applicable to virtual machine. And it 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).
+![logo](https://github.com/containerd/overlaybd/blob/main/docs/assets/overlaybd_icon_1x.png)
+
+Overlaybd (overlay block device) is a novel layering block-level image format, which is design for container, secure container and applicable to virtual machine. And it 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).
 
 Overlaybd is based on [PhotonLibOS](https://github.com/alibaba/PhotonLibOS), which is a high-efficiency LibOS framework.
 

docs/README.md

@@ -1,5 +1,7 @@
 # Overlaybd
 
+<img src="assets/overlaybd_icon_1x.png" class="pic"/>
+
 Overlaybd (overlay block device) is a novel layering block-level image format, which is design for container, secure container and applicable to virtual machine. And it 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).
 
 Overlaybd was first proposed by Alibaba Cloud and widely used in Alibaba cloud services. It became a sub-project of containerd in 2021.