doc: Align with v1.0 release

Unify the rst paragraph style.

Reword the introduction paragraphs for clarity.

Drop unneeded pages.

Add clarifications to the user guide.

Issue-Id: SCM-6584
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>
Change-Id: I84b60222b7f96f21e73b01683f5c185a34c8be69