Delay should be applied only once for an entry

[fabricereix]

For each entry, the request can be retried several times.
Currently the delay is applied before each request.
It should only be applied once before the first request.

Update doc from
--delay <MILLISECONDS> | Sets delay before each request
to
--delay <MILLISECONDS> | Sets delay before each entry

The delay before each retried request is set with the --retry-interval option.

[jcamiel]

Entry is maybe not very clear. Maybe we can be more explicit and refer retry ?

--delay <MILLISECONDS> | Sets delay before each request. The delay is not applied to retried request with --retry. See --retry-interval to space retried request.