Setup secrets for RPM release

[ronaldtse]

@ribose-jeffreylau could you help setup these secrets (org-wide):

• PACKAGE_SIGNING_KEY_BASE64
• GITHUB_YUM_DEPLOY_KEY_BASE64

Thanks!

Originally posted by @ronaldtse in https://github.com/rnpgp/rpm-spec-rnp/issues/7#issuecomment-629576614

[ribose-jeffreylau]

The following org-wide action secrets have been set up:

• PACKAGE_SIGNING_KEY_BASE64
• GHUB_YUM_DEPLOY_KEY_BASE64
  • The name GITHUB_YUM_DEPLOY_KEY_BASE64 is not allowed to be used, apparently.