Downstream guide

[lbarcziova]

Fixes #802 Fixes #825 Fixes #665

When reviewing, it is probably best to go commit by commit.

TODO:

• [ ] agree on the restructure
• [x] fix broken links (check also other repos)
• [x] create docs for CLI pull-from-upstream

RELEASE NOTES BEGIN

N/A

RELEASE NOTES END

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/packit-service/buildset/902a33f112cf421b924caceb5f66637a

:heavy_check_mark: pre-commit SUCCESS in 1m 15s

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/packit-service/buildset/3fcc47f844c9465e919a33428f61415a

:heavy_check_mark: pre-commit SUCCESS in 1m 15s

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/packit-service/buildset/f590d313e1c64b6b9c81b663d4bd730f

:heavy_check_mark: pre-commit SUCCESS in 1m 13s

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/packit-service/buildset/a7e4929724844d4ab128c8942208b3f5

:heavy_check_mark: pre-commit SUCCESS in 1m 14s

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/packit-service/buildset/2ae8a4aa9b11447aa7db5f2c567e70ca

:heavy_check_mark: pre-commit SUCCESS in 1m 11s

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/packit-service/buildset/2bb9857b84524b45a0928f7f05171c7a

:heavy_check_mark: pre-commit SUCCESS in 1m 14s

[softwarefactory-project-zuul[bot]]

Build succeeded (gate pipeline). https://softwarefactory-project.io/zuul/t/packit-service/buildset/f47b0829886745d399933acd54cb2822

:heavy_check_mark: pre-commit SUCCESS in 1m 16s

[softwarefactory-project-zuul[bot]]

Pull request merge failed: Resource not accessible by integration, You may need to manually rebase your PR and retry.