Editorial updates to common files, including sentence-style headings and consistency/clarity edits

Partial-Bug: #1250515

backport: havana

Resolved conflicts:
	doc/common/section_cli_openrc.xml
	doc/common/section_support-compute.xml

Change-Id: I9675dffd130c8aa6343143d9806adb4e0b74a55d
author: diane fleming
(cherry picked from commit bc7a9f0da7ca0b218cf54f5a8f3fc14a3f9f9391)
Merge "Editorial updates to common files, including sentence-style headings and consistency/clarity edits" into stable/havana