The tag is present in Lintian version 2.104.264. That is the most recent version we know about.
This package does not contain an md5sums control file. This control file listing the MD5 checksums of the contents of the package is not required, but if present debsums can use it to verify that no files shipped with your package have been modified. Providing it is recommended.
If you are using debhelper to create your package, just add a call to
dh_md5sums at the end of your binary-indep or binary-arch
target, right before