Created an readme for github

Just some temporary text to link users into simplesamlphp.org for download. Feel free to add more info later on.

Author: andreassolberg

README.md

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+SimpleSAMLphp
+=============
+
+This is the official repository of the SimpleSAMLphp software.
+
+* [SimpleSAMLphp homepage](https://simplesamlphp.org)
+* [SimpleSAMLphp Downloads](https://simplesamlphp.org/download)