Document new "dfuplus status" limit option

There is a new limit option to the dfuplus status command.  When status is done on a publisher dfu workunit, status is listed for the child dfu copy workunits.  The limit option controls the maximum number of child workunits listed.

I have defaulted the value to 1000 because publisher workunits can have a lot of children and the status command is used by automated tools.  The limit option will let the user list more or less child workunits as needed.

dfuplus server=http://eclwatch.hpccio.:8010 limit=300 action=status wuid=P20230301-123456