fix Desktop path error, revise main.py and update google writer tutorial

evaluation_examples/examples/libreoffice_impress/3b27600c-3668-4abd-8f84-7bcdebbccbdb.json

@@ -10,7 +10,7 @@
         "files": [
           {
             "url": "https://drive.usercontent.google.com/download?id=1aHMJzk2G8B_EqDlTAZLEiJ4h-ZsgA9UE&export=download&authuser=0&confirm=t&uuid=196a082d-5f08-4b3e-a64f-c021351f9cd8&at=APZUnTUXH4gvLvElvm9TtFhUJlIn:1705481007789",
-            "path": "Desktop/lec17-gui-events.pptx"
+            "path": "/home/user/Desktop/lec17-gui-events.pptx"
           }
         ]
       }
@@ -18,7 +18,7 @@
     {
       "type": "open",
       "parameters": {
-        "path": "Desktop/lec17-gui-events.pptx"
+        "path": "/home/user/Desktop/lec17-gui-events.pptx"
       }
     }
   ],
@@ -71,7 +71,7 @@
     },
     "result": {
       "type": "vm_file",
-      "path": "Desktop/lec17-gui-events.pptx",
+      "path": "/home/user/Desktop/lec17-gui-events.pptx",
       "dest": "lec17-gui-events.pptx"
     }
   }