reword "drag and drop some USFM files or folder to get started."

[sea-liesch]

maybe just "drag and drop some folders containing USFM" would be better. Or "drag and drop USFM folder." Since dragging and dropping individual files does not work.

[rbnswartz]

I would like it to have support for dragging usfm files into it but I didn't have time when I worked on it. I'll just change the wording until then.