Improve Maintainer Guidelines with regard to updating Fix Functions and Flux Commands

[TobiasNx]

We need to clarify the following:

• Is the published documentation repo and page referring to the lastest release or to the master?
• If to the master how do we tag functions and commands that are not part of the current release?
• What is the correct process for updating the documentation with regard to the Fix functions and Flux commands?
• Should we move the doc/Documentation-Maintainer-Guide.md to a top level Maintaining.md (see also Add example to string-decode and update documentation "how to publish" flux-commands.md #55)

If this is decided and clarified we need to document it to the https://github.com/metafacture/metafacture-documentation/blob/master/docs/Documentation-Maintainer-Guide.md

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Context:

As long as we had Metafacture Fix as a stand-alone repo the fix functions were documented in the README.md as well as copying the Fix Functions from the README to the metafacture-documentation repo when a release was published.

This was never formally documented but was a step in the Release TODO List since Release of 5.7.0: metafacture/metafacture-core#502

Also we had two different documentation states one referring to the master-branch in the README and one referring to the current release in the documentation repo.

Similar is the publication process for the Flux Commands the metafacture documentation repo referred to the current release because that was when the runner was published.

In context of #55 @dr0i questioned this approach and suggested updates to the process. See discussion starting here: #55 (comment)