[typo] An LLVM.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188589 91177308-0d34-0410-b5e6-96231b3b80d8
[lit] Rewrite TODO list, and elaborate on some things.

 - If anyone is interested in lit's feature set, I'd appreciate any comments on
   the elaborated items.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188590 91177308-0d34-0410-b5e6-96231b3b80d8