[docs] Mention the #pytest-asyncio:matrix.org chat room in README and for getting community support.

Signed-off-by: Michael Seifert <m.seifert@digitalernachschub.de>

Author: seifertm

README.rst

@@ -12,6 +12,9 @@ pytest-asyncio
     :alt: Supported Python versions
 .. image:: https://img.shields.io/badge/code%20style-black-000000.svg
     :target: https://github.com/ambv/black
+.. image:: https://img.shields.io/badge/Matrix-%23pytest--asyncio-brightgreen
+    :alt: Matrix chat room: #pytest-asyncio
+    :target: https://matrix.to/#/#pytest-asyncio:matrix.org
 
 `pytest-asyncio <https://pytest-asyncio.readthedocs.io/en/latest/>`_ is a `pytest <https://docs.pytest.org/en/latest/contents.html>`_ plugin. It facilitates testing of code that uses the `asyncio <https://docs.python.org/3/library/asyncio.html>`_ library.
 

docs/source/support.rst

@@ -18,4 +18,4 @@ If you require commercial support outside of the Tidelift subscription, reach ou
 
 Community support
 =================
-The GitHub page of pytest-asyncio offers free community support on a best-effort basis. Please use the `issue tracker <https://github.com/pytest-dev/pytest-asyncio/issues>`__ to report bugs and the `discussions <https://github.com/pytest-dev/pytest-asyncio/discussions>`__ to ask questions.
+The GitHub page of pytest-asyncio offers free community support on a best-effort basis. Please use the `issue tracker <https://github.com/pytest-dev/pytest-asyncio/issues>`__ to report bugs and the Matrix chat room `#pytest-asyncio:matrix.org <https://matrix.to/#/#pytest-asyncio:matrix.org>`__ or `GitHub discussions <https://github.com/pytest-dev/pytest-asyncio/discussions>`__ to ask questions.