Update the logging service documentation

The original page has a broken link and some overflowing underlines. Fix
these issues.
Reword the text to make it more readable and informative.

Change-Id: Ib10c7899a4fc0dfb227c434a2ff4f085763a8813
Signed-off-by: Gyorgy Szing <gyorgy.szing@arm.com>
1 file changed