Added modularize documentation.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@191091 91177308-0d34-0410-b5e6-96231b3b80d8
Added colon to make proper error message prefix.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@191092 91177308-0d34-0410-b5e6-96231b3b80d8