Document the bref/logger package

[mnapoli]

This PR documents and makes official the bref/logger package.

This package is a PSR-3 logger designed for AWS Lambda. In other words, it logs everything into stderr so that logs end up in CloudWatch.

This is a lightweight alternative to Monolog, and it is ready to use without having to configure Monolog handlers. It is also a bit more limited as it has no extension points.

[mnapoli]

This is a clarification on the current behavior regarding errors.

[miketheman]

I like the idea of a Cloudwatch specific logger.
Have you considered making the behavior configurable via env var, like other loggers?
I read https://laravel.com/docs/5.8/logging#configuration and thought it a clean approach for local dev vs deployed environment.

[mnapoli]

@miketheman When running locally with SAM or serverless it should work (because stderr is displayed in the console).

When running locally with php -S it will also work AFAIK.

So it should be good here!