message: Minor fixes to README.md (NFC)
  In particular fix the links to work on GitHub, and do not include RTTI to build.
diff: @@ -9,9 +9,9 @@ bring up new hardware, and improve usability for existing TensorFlow users.
  ## What is this doc?
  -Whereas the [MLIR draft specification](LangRef.md) discusses the details of the
  -IR in a dry style intended to be a long-lived reference document, this document
  -discusses higher level issues. This includes:
  +Whereas the [MLIR draft specification](g3doc/LangRef.md) discusses the details
  +of the IR in a dry style intended to be a long-lived reference document, this
  +document discusses higher level issues. This includes:
  * How we see the IR being used
  * How the compiler will be implemented
  * What capabilities the IR enables
  @@ -20,9 +20,10 @@ discusses higher level issues. This includes:
  For more information on MLIR, please see:
  -* [The MLIR draft specification](LangRef.md), which describes the IR itself,
  -* [The MLIR rationale document](Rationale.md), covering motivation behind some
  - decisions,
  +* [The MLIR draft specification](g3doc/LangRef.md), which describes the IR
  + itself,
  +* [The MLIR rationale document](g3doc/Rationale.md), covering motivation
  + behind some decisions,
  * previous external [talks](#talks),
  or join the [MLIR mailing list](https://groups.google.com/a/tensorflow.org/forum/#!forum/mlir).
  @@ -80,14 +81,16 @@ and by making references explicit with function_ref.
  # Getting started with MLIR
  +MLIR has been tested on Linux and MacOS, with a recent clang or with gcc 7.
  +
  ```
  git clone https://github.com/llvm/llvm-project.git
  -cd llvm/projects/
  +cd llvm-projects/llvm/projects/
  git clone https://github.com/tensorflow/mlir
  cd ../../
  mkdir build
  cd build
  -env CC=clang CXX=clang++ cmake -G Ninja -DLLVM_ENABLE_RTTI=1 ../llvm/
  +cmake -G Ninja ../llvm/
  ninja check-mlir
  ```
  