Add changelog

Author: asvetlov

README.rst

@@ -261,6 +261,7 @@ Changelog
 - Fixes a bug that prevents async Hypothesis tests from working without explicit ``asyncio`` marker when ``--asyncio-mode=auto`` is set. `#258 <https://github.com/pytest-dev/pytest-asyncio/issues/258>`_
 - Fixed a bug that closes the default event loop if the loop doesn't exist `#257 <https://github.com/pytest-dev/pytest-asyncio/issues/257>`_
 - Added type annotations. `#198 <https://github.com/pytest-dev/pytest-asyncio/issues/198>`_
+- Show asyncio mode in pytest report headers. `#266 <https://github.com/pytest-dev/pytest-asyncio/issues/266>`_
 
 0.17.0 (22-01-13)
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