Update README with MQTT authentication example

[eode]

Added example for MQTT broker authentication in README.

Description

Adds an authentication example.

Credit

License Acceptance

• This repository is Apache version 2.0 licensed and by making this PR, I am contributing my changes to the repository under the terms of the Apache 2 license.

Developer Certificate of Origin (DCO)

I agree with the DCO.

Type of changes

• Add/update a helper script
• Add/update link to an external resource like a blog post or video
• Bug fix
• New feature
• Test updates
• Text cleanups/updates
• New release to PyPi
• Documentation update

Checklist

• I have read the CONTRIBUTING document.
• I have signed off my commits per the DCO - I believe this was done automatically via github when I clicked "sign off"
• All new and existing tests pass (as long as they did before this commit, they still will)
• Agreements irrelevant to this PR have been removed

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[kratz00]

Thanks for the idea - I would prefer a short, general paragraph describing this feature. Only adding this information to the binary sensor, might be overlooked.