adding Sloan Foundation to sponsors page

Please update the sponsors page https://www.torproject.org/about/sponsors/ to have a new entry for Sloan Foundation. I have made these changes and would like for someone to make the changes live.

Here's the link https://gitlab.torproject.org/bekeela/tpo/-/blob/master/content/about/sponsors/Sloan%20Foundation/.gitkeep

Commit d5c9381fd11803aefd919d45958a9e66423b469c

Thank you!