[docs-only] search service readme

[fschade]

I wrote down what comes to mind about the search service, @mmattel please read what you think about it.
I haven't proofread much, please check for spelling mistakes too ;)

[mmattel]

@aduffeck @fschade can you have a look on the text if it is correct from a technical pov.
@EParzefall will do a language review.

[Jip-Hop]

Can the search service be disabled (temporarily)? @butonic mentions he has no search service running. Perhaps disabling search indexing would speed up initial upload.

[mmattel]

Can the search service be disabled (temporarily)? @butonic mentions he has no search service running. Perhaps disabling search indexing would speed up initial upload.

• The search service consumes events and does not block other tasks (no wait for finished indexing).
• When the search service runs on the same hardware, it is competing on ressources as all others do.
• Depending on the deployment method, services can be started and stopped individually. See the admin docs at General Info for more details. But it would not make sense to temporarily stop search as it gets info via the event bus when to trigger indexing, see the text in this repo for details.

[mmattel]

Note: with commit add resource deleted (many thanks for the info @aduffeck), item number 4 of the referenced issue #5515 is fixed. I will add a note there too.

[mmattel]

I will do a squash to ease backporting to 2.0.0 @kobergj