Update the main document of LLD for those who are not familiar with the project.
Update the main document of LLD for those who are not familiar with the project.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@296072 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld