Add instruction to list installed STRUCT packages in installation guide

Author: httpdss

docs/vhs/install.tape

@@ -67,5 +67,6 @@ Type "python3 -m venv venv" Sleep 500ms Enter
 Type "source venv/bin/activate" Enter
 Type "pip install git+https://github.com/httpdss/struct.git" Sleep 500ms  Enter
 Type "# STRUCT is now installed and ready to use" Enter
+Type "struct list" Enter
 
 Sleep 5s