add missing legal boilerplate to explorer

cdist/conf/type/__package_update_index/explorer/currage

@@ -1,4 +1,21 @@
-#!/bin/sh -e
+#!/bin/sh
+#
+# 2018 Thomas Eckert (tom at it-eckert.de)
+#
+# This file is part of cdist.
+#
+# cdist is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# cdist is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with cdist. If not, see <http://www.gnu.org/licenses/>.
 
 os="$("$__explorer/os")"