Update /? help for precompile

git-svn-id: http://protobuf-net.googlecode.com/svn/trunk@650 b72047a4-3652-0410-9617-b3994939e97b
r651

git-svn-id: http://protobuf-net.googlecode.com/svn/trunk@651 b72047a4-3652-0410-9617-b3994939e97b