Add upgrade notes for 1.16

docs/simplesamlphp-upgrade-notes-1.16.md

+Upgrade notes for SimpleSAMLphp 1.16
+====================================
+
+The class `SimpleSAML_Error_BadUserInnput` has been renamed to `SimpleSAML_Error_BadUserInput`.
+
+The `authmyspace` module has been removed since the service is no longer available.