Revise README for GitHub practice repository

Updated README to provide clearer instructions for practice repository.

Author: buduan

README.md

@@ -1,2 +1,9 @@
-# hello-github-for-cpu
-Hello.
+# 👋 Say hello to GitHub! 
+
+This is a practice repository for learning **Fork** and **Pull Request** on GitHub.
+
+## 🧩 What to do
+1. Fork this repository to your own GitHub account.
+2. Go to the `friends/` folder.
+3. Create a new file named **yourname.txt** (for example, `Baicen-Liu.txt`).
+4. Inside that file, write one line: