message: Simplify build instructions.
diff: @@ -92,13 +92,11 @@ has been tested on Linux and macOS, with recent versions of clang and with gcc 7
  ```
  git clone https://github.com/llvm/llvm-project.git
  -cd llvm-project/llvm/projects/
  -git clone https://github.com/tensorflow/mlir
  -cd ../..
  -mkdir build
  -cd build
  -cmake -G Ninja ../llvm -DLLVM_BUILD_EXAMPLES=ON -DLLVM_ENABLE_CXX1Y=Y
  -ninja check-mlir
  +git clone https://github.com/tensorflow/mlir llvm-project/llvm/projects/mlir
  +mkdir llvm-project/build
  +cd llvm-project/build
  +cmake -G Ninja ../llvm -DLLVM_BUILD_EXAMPLES=ON -DLLVM_ENABLE_CXX1Y=Y -DLLVM_TARGETS_TO_BUILD="host"
  +cmake --build . --target check-mlir
  ```
  As a starter, you may try [the tutorial](g3doc/Tutorials/Toy/Ch-1.md) on
  