GitLab

1) One space was missing from the indentation and, hence, rendering error
was generated in the user guide.
2) Partially reword Pointer Authentication related info.

Change-Id: Id5e65d419ec51dd7764f24d1b96b6c9942d63ba4
Signed-off-by: John Tsichritzis <john.tsichritzis@arm.com>