add documentation for file locking

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1550711 13f79535-47bb-0310-9956-ffa450edef68
add files

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1550712 13f79535-47bb-0310-9956-ffa450edef68