doc/rev-list-options: clarify "commit@{Nth}" for "-g" option

When "log -g" shows "HEAD@{1}", "HEAD@{2}", etc, calling
that "commit@{Nth}" is not really accurate. The "HEAD" part
is really the refname. By saying "commit", a reader may
misunderstand that to mean something related to the specific
commit we are showing, not the ref whose reflog we are
traversing.

While we're here, let's also switch these instances to use
literal backticks, as our style guide recommends. As a
bonus, that lets us drop some asciidoc quoting.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -252,9 +252,9 @@ list.
 +
 With `--pretty` format other than `oneline` (for obvious reasons),
 this causes the output to have two extra lines of information
-taken from the reflog.  By default, 'commit@\{Nth}' notation is
+taken from the reflog.  By default, `ref@{Nth}` notation is
 used in the output.  When the starting commit is specified as
-'commit@\{now}', output also uses 'commit@\{timestamp}' notation
+`ref@{now}`, output also uses `ref@{timestamp}` notation
 instead.  Under `--pretty=oneline`, the commit message is
 prefixed with this information on the same line.
 This option cannot be combined with `--reverse`.