Add note about MKIT_STUB_FILELIST and PREFIX

src/stub

             echo "     *  \`MKIT_STUB_FILELIST\` - List of full paths to"
             echo "        your files after installation."
             echo ""
+            echo "        Note that in case of debian/package.install files,"
+            echo "        PREFIX based paths (eg. /usr/bin) in this file should"
+            echo "        should be as if PREFIX was /usr."
+            echo ""
             echo "    Refer to these documents for further details:"
             echo ""
             echo "        http://rpm-guide.readthedocs.io/"