Ignore generated chart files

Change-Id: I05bf9b28c8cf100ec966b2a7637948a4097eedc8
diff --git a/.gitignore b/.gitignore
index 87ecf80..25e9198 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,8 @@
 /corpus/de_*-ud-train*
 /sandbox
 /Sandbox
+/charts/*.pdf
+/charts/*.png
 /output_*
 /corpus/*.txt
 \#*