Added: Add GitHub Secure Open Source Fund sponsors logo

- https://resources.github.com/github-secure-open-source-fund
- https://github.blog/open-source/maintainers/securing-the-supply-chain-at-scale-starting-with-71-important-open-source-projects
- https://termux.dev/en/posts/general/2025/08/11/termux-selected-for-github-secure-open-source-fund-session-2.html

The `github.png` logo is sourced from https://github.com/logos