Update README.md

[stacksjb]

Updating open on Mac OS X with easier steps to bypass quarantine/Unsigned app

Pre-flight Checklist

1. Please remember that if you are logging a bug for some service that has stopped working or is working incorrectly, please log the bug here
2. If you are requesting support for a new service in Ferdium, please log it here
3. Please remember to read the self-help documentation - in case it helps you unblock yourself for issues related to older versions of recipes that were installed on your machine. (These will get automatically upgraded when you upgrade to the newer versions of Ferdium, but to get new recipes between Ferdium releases, this documentation is quite useful.)
4. Please ensure you've completed all of the following.

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Description of Change

Simply updates the "Unsigned" section for Mac with an easier method for those who are not familiar with unsigned.

Motivation and Context

Not all users are comfortable or familiar with the command line -

Checklist

• My pull request is properly named
• The changes respect the code style of the project (npm run prepare-code)
• npm test passes
• I tested/previewed my changes locally

Release Notes

[vraravam]

@all-contributors please add @stacksjb for doc

[allcontributors]

@vraravam

I've put up a pull request to add @stacksjb! 🎉