Explain what is wrong with cabal.sub-rs.test.hs

cabal-testsuite/PackageTests/SDist/Respect-Project-File/Projects-Default-Yes/cabal.sub-rs.test.hs

@@ -1,4 +1,12 @@
 import Test.Cabal.Prelude
 
+-- cabal.sub-rs.project has "packages: r/ s/" but "cabal sdist" writes
+-- sdist/p-0.1.tar.gz and sdist/q-0.1.tar.gz instead of the expected
+-- sdist/r-0.1.tar.gz and sdist/s-0.1.tar.gz. That is wrong, "cabal sdist"
+-- should respect the "--project-file" option but instead picks up the default
+-- "cabal.project" that has "packages: p/ q/".
+--
+-- TODO: Fix this behaviour and apply the patch cabal.sub-rs.patch to update the
+-- expected output to what we'd expect if "cabal sdist" respected the project.
 main = cabalTest . withProjectFile "cabal.sub-rs.project" $ do
     cabal "sdist" ["all"]