Documentation for RIVER-DROPS-Date_from and Date_to needs format required and example

The documentation at https://wiki.ushahidi.com/display/WIKI/SwiftRiver+API+River+Resources#SwiftRiverAPIRiverResources-GETrivers/:id/drops
needs to describe the date format for the "date_from" and "date_to" parameters and provide and example.

Tried there three but none worked: mm/dd/yyyy, yyyy/mm/dd, RFC822, i.e. "Thu, 25 Jul 2013 15:12:33 -0700"
