message: Document compiler requirements
  Fixes
diff: @@ -21,7 +21,8 @@ languages.
  Verible's code base is written in C++.
  -To build, you need the [bazel] build system.
  +To build, you need the [bazel] build system and a C++17 compatible compiler
  +(e.g. >= g++-7; Using clang currently fails to compile the m4 dependency).
  ```bash
  # Build all tools and libraries
  