change sections order in ECMWF tutorial

[sbrunato]

change sections order in ECMWF tutorial

From:

• Search (build download request)
  • Search from an existing product type
  • Search using a custom MARS request:
• Send product retrieval request and download when available
  • configure credentials
  • download
• Open dataset with xarray and cfgrib, then plot using matplotlib

To:

• configure credentials
• Search (build download request) from an existing product type
• Send product retrieval request and download when available
• Open dataset with xarray and cfgrib, then plot using matplotlib

To go further:

• Advanced search using a custom MARS request