Doc additions

[norg]

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• I have read the contributing guide lines at https://docs.suricata.io/en/latest/devguide/codebase/contributing/contribution-process.html
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• I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

Link to redmine ticket:

Describe changes:

• minor doc addition to make cpu affinity settings more clear (priority can overwrite)
• minor doc addition to highlight that dataset type is mandatory

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[github-actions]

NOTE: This PR may contain new authors:

Andreas Herz <andreas@stamus-networks.com>

[jufajardini]

The form looks good to me. :)

[victorjulien]

Merged in #9312, thanks!