Fix missing import in docs (#161)

missing import: `from fastapi_contrib.tracing.utils import setup_opentracing` for the jaeger tracing example

Author: Daniel Dubovski

README.rst

@@ -245,6 +245,7 @@ To setup Jaeger tracer and enable Middleware that captures every request in open
 
  from fastapi import FastAPI
  from fastapi_contrib.tracing.middlewares import OpentracingMiddleware
+ from fastapi_contrib.tracing.utils import setup_opentracing
 
  app = FastAPI()