Docs: Update the required build packages for fedora based systems.

Description

I was following the installation docs 1.1.3+176.g9defbb6 and noticed there was a build dependency missing, at least for Fedora 28 haven't tried the others.

When trying to build ruamel.yaml it would error and complain about Python.h missing.

I am not sure how this was not caught by the Fedora 27 CI job. I suspect that something previously might have been pulling python3-devel as a dependency and that was later dropped when the packages were upgraded in Fedroa 28. Although I haven't investigated further.

Changes proposed in this merge request:

• Added python3-devel as build requirement in the fedora installation docs.

This merge request, when approved, will close issue/bug:

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