add curl detail log to stderr, update readme about key Role requirement

[yurenchen000]

1. output will like this:

===get http://xxxx/api/search?query=&
zzzz.json
===get http://xxxx/api/dashboards/db/yyyy
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 15719    0 15719    0     0  81869      0 --:--:-- --:--:-- --:--:-- 81869

2. readme update:
   key role require admin for datasources export