Add .gitattribute file and set lf for one sample-file, see bug 61609

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1819771 13f79535-47bb-0310-9956-ffa450edef68

.gitattributes

@@ -0,0 +1 @@
+test-data/hmef/quick-contents/quick.html text eol=lf