Update this manuscripts thumbnail

[vincerubinetti]

Hello Manubot user.

If you were not already aware, your paper is being showcased in the Manubot Catalog.

Previously, we were making our own thumbnails for each paper, and hosting them in the same repository as manubot.org. But now we are moving to a system of having each paper store its thumbnail in its own repository, and linking to it from there.

Here is our suggested thumbnail for your paper that follows the new thumbnail guidelines:

Please place this image in the root of your repository with the name thumbnail.png. Once you have, let us know in this issue and we'll do the rest to update the catalog.