top: expand on column highlight quirks in man document
Confession is supposed to be good for the sole, right?
After a senior moment regarding the 'x' toggle quirks,
and thinking top had somehow regressed, I concluded an
additional explanatory note might well be appropriate.
Those quirks were already documented under the 5d & 5e
topics. But there was no such caution documented under
the 'x' command explanation itself, found in topic 4c.
Signed-off-by: Jim Warner <james.warner@comcast.net>