Add .gitattribute to make sure pdf are treated as binary

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..d72fd52
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1 @@
+*.pdf binary