Ship a README with packages

[IgorTodorovskiIBM]

Currently, we ship a .env file as well as the package contents.

The README should contain:

• A description of the package
• Instructions on how to source the .env file
• Any z/OS extensions that need to be highlighted
• Known issues

We can extend zopen-build to pick up the README.md from the repo.

Anything else?

FYI @MikeFultonDev

[IgorTodorovskiIBM]

Related starter PR for this: https://github.com/ZOSOpenTools/utils/pull/110/files