Added kroki.io to diagramming chapter

[larkly]

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• [x] Your additions are Free software
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Please take some time to answer the following questions as best you can:

• Why is it awesome?

It's very useful for sysadmins to document with textual diagrams from i.e. Gitlab or other instances supporting Kroki. While the Kroki instance can be somewhere else, it's very useful to self host for sensitive diagrams.

• Have you used it? For how long?

I've used it for about a year or so.

• Is this in a personal or professional setup?

Professional and personal.

• How many devices/users/services/... do you manage with it?

Unknown, it's used by the people who create PlantUML or other types of diagrams in Gitlab. Personally I also use it in my static website blog (mkdocs supports Kroki)

• Biggest pros/cons compared to other solutions?

Except PlantUML there are no other solutions other than systems supporting this themselves.

• Any other comments about your use case, things you've found excellent, limitations you've encountered... ?

[xrat]

Quite impressed! I did not know about Kroki before, had a look just now, and I am thankful for the pull request. IMO, Kroki would be a worthwhile addition to the list.

I wonder whether it should follow #416, though, and link to yuzutech/kroki!?