doc: detailed steps of syncing fork

Author: AlaRduTP

lab3/README.md

@@ -7,7 +7,9 @@ In this lab, you will write unit tests for functions implemented in `main.js`. Y
 ## Preparation (Important!!!)
 
 1. Sync fork your branch (e.g., `SQLab:311XXXXXX`)
-2. `git checkout -b lab3` (**NOT** your student ID !!!)
+2. `git checkout 311XXXXXX`
+3. `git pull`
+4. `git checkout -b lab3` (**NOT** your student ID !!!)
 
 ## Requirement