Update changelog

CHANGELOG.rst

@@ -8,6 +8,8 @@ Bug Fixes
   and TokenAwarePolicy is not in use
 * Avoid registering multiple atexit() cleanup functions will the
   asyncore event loop is restarted multiple times
+* Delay initialization of reactors in order to avoid problems
+  with shared state when using multiprocessing (PYTHON-60)
 
 2.0.1
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