Schema licensing

* All the same as GPG/GPGME, plus added Apache 2.0.

lang/xml-schemas/README.txt

@@ -0,0 +1,29 @@
+===========
+XML Schemas
+===========
+
+The XML schemas in this directory are available under the same terms
+as GPGME (i.e. the GPL 2 or later or the LGPL 2.1 or later), or
+alternatively the Apache 2.0 license.
+
+The schemas were generated with oXygenXML Editor 17.1 (mentioning that
+isn't necessary, but might be helpful).
+
+
+--------------
+Apache license
+--------------
+
+Copyright © Benjamin D. McGinnes, 2016
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.