First, try making a files
subdirectory in your wiki, and putting your files in there.
I tried using an html anchor tag
<a href="files/file.csv" download="file.csv">download this</a>
instead of the markdown link syntax
[download this](files/file.csv)
but it seems that GitHub wiki strips out the download attribute from the anchor tag.
In the end, I zipped my spreadsheet in a zip file and had the markdown link point to the zip file.
[download this](files/file.csv.zip)
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…