Add Apache copyright NOTICE

Change-Id: Iaf7b2f7f15ef53d2a55ac3986b9beb236421df7a
diff --git a/src/main/java/de/ids_mannheim/korap/tokenizer/NOTICE b/src/main/java/de/ids_mannheim/korap/tokenizer/NOTICE
new file mode 100644
index 0000000..2ef39b3
--- /dev/null
+++ b/src/main/java/de/ids_mannheim/korap/tokenizer/NOTICE
@@ -0,0 +1,2 @@
+The Span class contains code from OpenNLP developed at
+The Apache Software Foundation (http://www.apache.org/).