Remove `-ptr` from the help output of `service create`

This fix is based on the comment:
https://github.com/docker/docker/pull/28147#discussion_r86996347

Previously the output string of the `DurationOpt` is `duration-ptr`
and `Uint64Opt` is `uint64-ptr`. While it is clear to developers,
for a normal user `-ptr` might not be very informative.

On the other hand, the default value of `DurationOpt` and `Uint64Opt`
has already been quite informative: `none`. That means if no flag
provided, the value will be treated as none.
(like a ptr with nil as the default)

For that reason this fix removes the `-ptr`.

Also, the output in the docs of `service create` has been quite
out-of-sync with the true output. So this fix updates the docs
to have the most up-to-date help output of `service create --help`.

This fix is related to #28147.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

opts/opts.go

@@ -345,7 +345,7 @@ func (c *NanoCPUs) Set(value string) error {
 
 // Type returns the type
 func (c *NanoCPUs) Type() string {
-	return "NanoCPUs"
+	return "decimal"
 }
 
 // Value returns the value in int64