Write a blog post about downstream jobs targeting Fedora package maintainers

[nforro]

We do have Fedora releases guide but Fedora maintainers are still getting confused by seeing upstream jobs mentioned. Write a blog post that:

• [ ] demonstrates a basic configuration (pull_from_upstream, koji_build, bodhi_update) in dist git
• [ ] explains how to verify the config with CLI, how to test/run locally
• [ ] explains how/when the jobs are triggered by the service, how to trigger them manually
• [ ] explains issue_repository
• [ ] does not mention propose_downstream or any other upstream jobs

As a bonus:

• [ ] explains why upstream_project_url is needed (and upstream_tag_template)

[lbarcziova]

I would lean towards having this as a part of "regular docs" and not a blogpost, probably as a subsection of Fedora releases guide.

[nforro]

Making it part of the docs definitely makes sense, a blogpost was just the first thing that came to mind.