Document bulk record create request

[katrinDY]

Notes

• Email: API Bulk Record Insert
• This task is from an email thread and that's the reason why Tomaž will take over this. (Also explains the lack of more context for this issue)

TODO

• [ ] document feature
• [ ] update client when finished

[tjerman]

Someone already documented this to the point where it's sufficient so I'll mark it off as done. The contents are here