Add systemd unit as user contrib

[samveen]

Reduce the time to deploy by contributing my starter systemd unit and associated install instructions, to save new users the time of building up everything from scratch.

Note: This could probably be included as common underlying sources if, as and when kafdrop gets included into packaging systems by linux distributions further downstream. I could also contribute packaging information for rpm and deb formats, if that's something that'll be useful.

[Bert-R]

@davideicardi Are you familiar with this matter and able to review this PR?

[davideicardi]

@samveen Thank you!

It looks a good contribution to me. Just some small suggestions:

• Rename contrib/systemd/README.syste.md to contrib/systemd/README.md
• Add a small introduction regarding systemd and when to use it. Maybe something similar to what you have written inside the PR description.
• In which Linux distribution do you have tested it? Maybe it could be useful to specify it and explain that in other distributions some changes could be necessary

The validate action is failing, but it should be something else. I will investigate.

[davideicardi]

Thank you! See my comment.

[samveen]

@davideicardi Please review.

* Rename `contrib/systemd/README.syste.md` to `contrib/systemd/README.md`

Done (even though it takes away that small bit of pun fun in the name).

* Add a small introduction regarding systemd and when to use it. Maybe something similar to what you have written inside the PR description.
* In which Linux distribution do you have tested it? Maybe it could be useful to specify it and explain that in other distributions some changes could be necessary

Added to relevent sections in README.md

The validate action is failing, but it should be something else. I will investigate.

The linter failure was due to long lines in the README.md . It's fixed.

[davideicardi]

@samveen
Ah sorry, I just understand now the name joke :-) !
In this case we can leave the original name if you prefer!

[davideicardi]

Thank you!

[samveen]

@samveen Ah sorry, I just understand now the name joke :-) ! In this case we can leave the original name if you prefer!

I'll leave it as is. The auto-magic display of README.md on the Github web interface is better than making a joke with the name README.syste.md. Not to mention removing the need for another round of approvals 🤣