message: Update the contributing guide to point to C++ issues
diff: -Azure SDK for C Contributing Guide
  +Azure SDK for C++ Contributing Guide
  -------------------------------------
  -Thank you for your interest in contributing to Azure SDK for C.
  +Thank you for your interest in contributing to Azure SDK for C++.
  -- For reporting bugs, requesting features, or asking for support, please file an issue in the [issues](https://github.com/Azure/azure-sdk-for-c/issues) section of the project.
  +- For reporting bugs, requesting features, or asking for support, please file an issue in the [issues](https://github.com/Azure/azure-sdk-for-cpp/issues) section of the project.
  - If you would like to become an active contributor to this project please follow the instructions provided in [Microsoft Azure Projects Contribution Guidelines](http://azure.github.com/guidelines.html).
  