Indicate removal of tmpdir after failed build

app/ghcup/Main.hs

@@ -750,7 +750,8 @@ Check the logs at ~/.ghcup/logs and the build directory #{tmpdir} for more clues
                       VLeft (V (BuildFailed tmpdir e)) ->
                         runLogger
                             ($(logError) [i|Build failed with #{e}
-Check the logs at ~/.ghcup/logs and the build directory #{tmpdir} for more clues.|]
+Check the logs at ~/.ghcup/logs and the build directory #{tmpdir} for more clues.
+Make sure to clean up #{tmpdir} afterwards.|]
                             )
                           >> exitFailure
                       VLeft e ->