message: Update Contributing.md doc to refer to the developer guide
  This intends to reduce duplication and ensure that new informations added
  to the developer guide (like the recent testing good practice) are not
  missed by new contributors.
diff: @@ -33,12 +33,12 @@ If you want to contribute, start working through the MLIR codebase, navigate to
  ### Contribution guidelines and standards
  -* Follow coding style (see below).
  +* Read the [developer guide](g3doc/DeveloperGuide.md).
  * Ensure that you use the correct license. Examples are provided below.
  * Include tests when you contribute new features, as they help to a)
  prove that your code works correctly, and b) guard against future breaking
  changes to lower the maintenance cost.
  -* Bug fixes also generally require unit tests, because the presence of bugs
  +* Bug fixes also generally require tests, because the presence of bugs
  usually indicates insufficient test coverage.
  #### License
  @@ -47,8 +47,3 @@ Include a license at the top of new files.
  * [C/C++ license example](https://github.com/tensorflow/mlir/blob/master/examples/toy/Ch1/toyc.cpp)
  * [Python license example](https://github.com/tensorflow/mlir/blob/master/bindings/python/test/test_py2and3.py)
  -
  -#### C++ coding style
  -
  -Changes to MLIR C++ code should conform to
  -[LLVM Coding standards](https://llvm.org/docs/CodingStandards.html).
  