ticket:10179: Add documentation to TestLocaleStructure explaining that it validates each locale .txt file against the golden structLocale.txt file so that developers know that to fix this test means adding the templates for any new data to structLocale.txt

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk@33778 251d0590-4201-4cf1-90de-194747b24ca1