doc: Normalize the files and commands paths

Normalize the files and commands paths from the project checkout root
directory.

Also, take the opportunity to apply the 80 chars line size where applicable.

Issue-Id: SCM-2575
Signed-off-by: Diego Sueiro <diego.sueiro@arm.com>
Change-Id: Idcdfe5b35f5853e261f4ee15819a4d42a848701f