Add 'clef=bass' into the converted output.

This doesn't affect output from abcm2ps, which assumes bass clef for a middle=D,
but I like the idea of being more explicit.

makeCello.sh

@@ -33,5 +33,5 @@ find $booke -name "*.abc" | sort |
             middle="D"
         fi
         name=`basename $filename .abc`
-        sed -e "/^ *K:/s/$/ middle=$middle/" $filename > $outdir/$name.abc
+        sed -e "/^ *K:/s/$/ clef=bass middle=$middle/" $filename > $outdir/$name.abc
     done