Tell git to ignore the Quilt internal directory in package/config

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/config/.gitignore

@@ -21,3 +21,8 @@ nconf
 qconf
 gconf
 kxgettext
+
+#
+# Quilt is being used to handle the patch series
+#
+.pc