* Added functionality to crash the build during CI whenever linter warnings are encountered.
* Updated the docs with a description on how to use the build in CI
* Fixed small typo
* Fixed description of build error.
In the `create-react-app` command, try to install packages using Yarn.
If Yarn is not installed, use npm instead.
In `react-scripts`, detect if the project is using Yarn by checking if
a `yarn.lock` file exists. If the project is using Yarn, display all
the instructions with Yarn commands and use Yarn to install packages
in `init` and `eject` scripts.