Update README.md - fix debug tags
Update README.md - fix debug tags

Based on the following file, I believe that `debug` should be added as a prefix rather than a suffix.
https://github.com/GoogleContainerTools/distroless/blob/b19f550dce74b65e09706e46fc82c0075434f563/BUILD#L29

GoogleContainerTools/distroless,GoogleContainerTools/distroless,GoogleContainerTools/distroless