Update bug_report.yml

Some user don't now how to upload 3mf file. Make the description more clear.

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -99,7 +99,7 @@ body:
     id: file_uploads
     attributes:
       label: Project file & Debug log uploads
-      description:  Drop the project file and debug log here
+      description:  Drop the project file(a ZIP archive containing 3mf file) and debug log here
       placeholder: |
         Project File: `File` -> `Save project as...` then zip it & drop it here
         Log File:  `Help` -> `Show Configuration Folder`, then zip the log directory, or just select the newest logs in `log` when this issue happens and zip them, then drop the zip file here