message: bazel: update README for OS X
diff: @@ -33,11 +33,19 @@ On Ubuntu, run the following commands:
  apt-get install realpath
  ```
  -On OS X, you'll need to install realpath. This can be accomplished via Homebrew:
  +On OS X, you'll need to install several dependencies. This can be accomplished via Homebrew:
  ```
  brew install coreutils # for realpath
  +brew install wget
  +brew install cmake
  +brew install libtool
  +brew install go
  +brew install bazel
  ```
  +Envoy compiles and passes tests with the version of clang installed by XCode 8.3.3:
  +Apple LLVM version 8.1.0 (clang-802.0.42).
  +
  3. Install Golang on your machine. This is required as part of building [BoringSSL](https://boringssl.googlesource.com/boringssl/+/HEAD/BUILDING.md)
  and also for [Buildifer](https://github.com/bazelbuild/buildtools) which is used for formatting bazel BUILD files.
  4. `bazel fetch //source/...` to fetch and build all external dependencies. This may take some time.
  