README: Show the architecture picture

Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

README.md

@@ -6,6 +6,8 @@
 ---
 
 ## Components
+![architecture](design/architecture.png)
+
 ### rune
 `rune` is a CLI tool for spawning and running enclaves in containers according to the OCI specification. The codebase of `rune` is a fork of [runc](https://github.com/opencontainers/runc), so `rune` can be used as `runc` if enclave is not configured or available.