Docs: Change image compression site recommendation

doc/development/documentation/styleguide.md

@@ -542,7 +542,7 @@ To indicate the steps of navigation through the UI:
   a valid name for an illustration is `devops_diagram_v11_1.png`.
 - Keep all file names in lower case.
 - Consider using PNG images instead of JPEG.
-- Compress all images with <https://tinypng.com/> or similar tool.
+- Compress all images with <https://pngquant.org/> or similar tool.
 - Compress gifs with <https://ezgif.com/optimize> or similar tool.
 - Images should be used (only when necessary) to _illustrate_ the description
   of a process, not to _replace_ it.