improve gitignore

.gitignore

-*/input/
-*/tmp/
-*/output/
-wikipedia_to_hdoc/result/*
-wikipedia_to_hdoc/tmp/*
-wikipedia_to_hdoc/hdoc_to_opale/tmp/*
-wikipedia_to_hdoc/output/*
\ No newline at end of file
+*/input/*
+*/tmp/*
+*/output/*
+!*/input/sample.*
\ No newline at end of file