Add cynkra bronze sponsor (go-gitea#21325)

@techknowlogick 

Only added a placeholder, the index is possibly wrong. But I think you
need to do/finalize that as the opencollective holder :)

You can take the logo of the opencollective account. LMK if I can help
more!

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <matti@mdranta.net>

README.md

@@ -151,6 +151,7 @@ Support this project by becoming a sponsor. Your logo will show up here with a l
 <a href="https://opencollective.com/gitea/sponsor/7/website" target="_blank"><img src="https://opencollective.com/gitea/sponsor/7/avatar.svg"></a>
 <a href="https://opencollective.com/gitea/sponsor/8/website" target="_blank"><img src="https://opencollective.com/gitea/sponsor/8/avatar.svg"></a>
 <a href="https://opencollective.com/gitea/sponsor/9/website" target="_blank"><img src="https://opencollective.com/gitea/sponsor/9/avatar.svg"></a>
+<a href="https://cynkra.com/" target="_blank"><img src="https://images.opencollective.com/cynkra/logo/square/64/192.png"></a>
 
 ## FAQ