Revisit CONTRIBUTING.md
📚 Documentation
Update CONTRIBUTING.md to include detailed steps and missing guidelines Pytorch-Lightning developer machine setup. The setup instructions are currently under "Testing" section, and they don't have information about all the necessary dependencies. We should rename the section to make it easy for developers to find it, add missing steps, as well as add debugging/testing/troubleshooting guidelines.
A good example to follow is Pytorch CONTRIBUTING.md.
Some of the missing steps I and my colleagues learned while setting up Pytorch-Lightning for development on local machine:

Install dependencies from requirements.txt (I am new to OSS development, and didn't run "pip install -r requirements.txt", directly went to "Testing" instructions and ran commands from there, resulting into later having to install bunch of dependencies manually after running "make test" and getting bunch of test failures).
brew install cmake
brew install libuv
brew install pkg-config
After the setup, I still ran into errors, and had to manually install torch.