Create README.md for openy_hf

[froboy]

Original Issue, this PR is going to fix: no issue

From a thread on Slack: https://openy.slack.com/archives/C6G4ZTLVC/p1599579039167800

Make sure these boxes are checked before asking for review of your pull request - thank you!

If there is a new feature or this is a bug fix - use 8.x-2.x branch. We'll tag for release if the bug is critical asap or tag for release next bug fix release until critical issue arrived.

Steps for review

• Read
• Confirm that the configuration setting steps are correct.

General checks

• All coding styles are fulfilled and there are no any issues reported by CodeSniffer. See Code of Conduct.
• Documentation has been updated according to PR changes.
• Steps for review have been provided according to PR changes.
  
• Make sure you've provided all necessary hook_update_N to support upgrade path.
• Make sure your git email is associated with account on drupal.org, otherwise you won't get commits there.
  
• If you would like to get credits on drupal.org, check documentation.

Thank you for your contribution!

[gundevel]

Can one of the admins verify this patch? Use "o+k to test" or ''t+est this please" for manual build execution.