update readme with deprecation warning

Author: smithclay

README.md

@@ -1,5 +1,7 @@
 # lightstep-tracer-python
 
+> ❗ **This instrumentation is no longer recommended**. Please review [documentation on setting up and configuring the OpenTelemetry Python Launcher](https://github.com/lightstep/otel-launcher-python) for more information on migrating to OpenTelemetry.
+
 [![PyPI](https://img.shields.io/pypi/v/lightstep.svg?maxAge=2592000)]() [![Circle CI](https://circleci.com/gh/lightstep/lightstep-tracer-python.svg?style=shield)](https://circleci.com/gh/lightstep/lightstep-tracer-python) [![MIT license](http://img.shields.io/badge/license-MIT-blue.svg)](http://opensource.org/licenses/MIT)
 
 The LightStep distributed tracing library for Python.