Update README.md

Author: clutchski

README.md

@@ -2,7 +2,19 @@
 
 [![CircleCI](https://circleci.com/gh/DataDog/dd-trace-py.svg?style=svg&circle-token=f9bf80ce9281bc638c6f7465512d65c96ddc075a)](https://circleci.com/gh/DataDog/dd-trace-py)
 
-## Testing
+## Versions
+
+Tracing client libraries will follow [semver](http://semver.org). While we are less than version 1.0,
+we'll increment the minor version number for backwards incompatible and significant changes. We'll
+increment the bugfix version for other changes.
+
+This library is in beta so please pin your version numbers and do phased rollouts.
+
+[changelog](https://github.com/DataDog/dd-trace-py/releases)
+
+## Development
+
+### Testing
 
 The test suite requires many backing services (PostgreSQL, MySQL, Redis, ...) and we're using
 ``docker`` and ``docker-compose`` to start the service in the CI and in the developer machine.
@@ -13,7 +25,7 @@ You can launch the test matrix using the following rake command::
 
     $ rake test
 
-## Benchmark
+### Benchmarks
 
 When two or more approaches must be compared, please write a benchmark in the ``tests/benchmark.py``
 module so that we can keep track of the most efficient algorithm. To run your benchmark, just::