In demo, add button which uses an example XLS file, like the one in the scr

Directory Spreadsheet
1

In demo, add button which uses an example XLS file, like the one in the screenshot, so that I don’t have to search for such files to test the demo.
Also, the default size for a new sheet could be 20 rows 10 columns, just to make something visible.

2

Default size is now 50x8