[Docs] Beats upgrade and permissions

[leehinman]

Beats upgrading doc currently has:

beats/libbeat/docs/upgrading.asciidoc

Lines 17 to 21 in a6aa347

	As a general rule, you can upgrade between minor versions (for example, 8.x to
	8.y, where x < y) by simply installing the new release and restarting the Beat
	process. {beats} typically maintain backwards compatibility for configuration
	settings and exported fields. Please review the
	<<release-notes,release notes>> for potential exceptions.

We should add to it that if assets have changed (dashboards, pipelines, index templates, etc), then it will be necessary to run at least once with permissions that can do the setup operations.

[rehanpfmr]

@leehinman
Can this be assigned to me? I will try to update the doc.