Update README

Signed-off-by: Kotaro Inoue <k.musaino@gmail.com>

Author: musaprg

README.md

@@ -2,6 +2,8 @@
 
 A toy container runtime written in Zig.
 
+CAUTION: still under active development, not production ready.
+
 ## Prerequisites
 
 CAUTION: Zig language is still under active development, so building with the latest zig release might fail.
@@ -32,5 +34,7 @@ zig build -Drelease-safe
 
 ## Similar projects
 
-- [fancl20/zrun](https://github.com/fancl20/zrun) A fast and low-memory footprint (non-standard) container runtime fully written in Zig.
+- [opencontainers/runc](https://github.com/opencontainers/runc) CLI tool for spawning and running containers according to the OCI specification
 - [containers/youki](https://github.com/containers/youki) A container runtime written in Rust
+- [containers/crun](https://github.com/containers/crun) A fast and lightweight fully featured OCI runtime and C library for running containers
+- [fancl20/zrun](https://github.com/fancl20/zrun) A fast and low-memory footprint (non-standard) container runtime fully written in Zig.