Merge pull request #82 from OCR-D/alto4-cc

ALTO is published as CC-BY-SA 4.0 now

README.md

@@ -238,7 +238,7 @@ This is free software. You may use it under the terms of the [MIT License](LICEN
 
 During the installation process several projects are included (in [`./vendor`](./blob/master/vendor)). These projects have different licenses:
 * [Saxon HE 9.7](http://saxon.sourceforge.net/#F9.7HE), [`MPL`](https://www.mozilla.org/MPL/).
-* [ALTOXML schema](https://github.com/altoxml/schema), [`Open Source`](https://github.com/altoxml/schema/issues/37#issuecomment-218730230)
+* [ALTOXML schema](https://github.com/altoxml/schema), ["Open Source"](https://github.com/altoxml/schema/issues/37#issuecomment-218730230) for ALTO <= 3.1, [`CC BY SA 4.0`](https://creativecommons.org/licenses/by-sa/4.0/legalcode) since ALTO 4.0
 * [PAGE schemas](http://www.primaresearch.org/schema/PAGE/gts/pagecontent/), `?`
 * [xsd-validator](https://github.com/kba/xsd-validator) by Adrian Mouat [@amouat](https://github.com/amouat), `Apache 2.0`
 * ABBYY FineReader XSD, `?`