add Composer and Packagist to release process

[jeffpaul]

Is your enhancement related to a problem? Please describe. On most plugins we include a composer.json file, but we don't always submit a package to Packagist. Let's update our docs to confirm that as part of the process with specific steps on how to do so.

Describe the solution you'd like

• [ ] add composer.json details to Release Process
• [ ] add Packagist details to Release Process

Designs n/a

Describe alternatives you've considered none

Additional context n/a