Add {fmt} to Thrift dependencies in README
Add {fmt} to Thrift dependencies in README

Summary: D14954926 migrated from Folly Format to {fmt}, so update README accordingly.

Differential Revision: D15299569

fbshipit-source-id: f0350cbc01cc451dcdf89e0dbfecd749ef145281

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift