[doc] add C++ to the README
[doc] add C++ to the README

Summary: Duh!

Reviewed By: dulmarod

Differential Revision: D7443714

fbshipit-source-id: 319aa5c

jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer