docs(readme): show how to interact with the shell

Author: Celve

readme.md

@@ -1,15 +1,19 @@
 # recore
+
 A simple RISC-V kernel, which could be seen as a incomplete reimplementation of [rCore-Tutorial-v3](https://github.com/rcore-os/rCore-Tutorial-v3).
 
 ## Features
+
 - concurrency of multiple processes, each of which contains mutiple native threads
 - dynamic memory management in kernel supported by SLUB
 - virtual memory with SV39
 - a simple file system with a block cache
 - an interactive shell in the userspace that supports some basic commands
 
 ## Run
+
 To run this kernel, you should:
+
 ``` bash
 $ git clone [email protected]:Celve/recore.git
 $ cd recore/kernel
@@ -19,6 +23,8 @@ $ make run
 
 There should be an interactive shell that provide similar interface like the normal shell on your operating system. Use it to explore the functionality of this simple OS.
 
+Supported shell commands are listed in `user/src/bin`, or use `ls` in shell to list.
+
 ## Wiki
 
 For more details, please check the [wiki](https://github.com/Celve/recore/wiki).