PYTHON-3015 Document cipher mismatch issues (#791)

Author: behackett

doc/examples/tls.rst

@@ -213,3 +213,21 @@ revocation checking failed::
   [('SSL routines', 'tls_process_initial_server_flight', 'invalid status response')]
 
 See :ref:`OCSP` for more details.
+
+Python 3.10+ incompatibilities with TLS/SSL on MongoDB <= 4.0
+.............................................................
+
+Note that `changes made to the ssl module in Python 3.10+
+<https://docs.python.org/3/whatsnew/3.10.html#ssl>`_ may cause incompatibilities
+with MongoDB <= 4.0. The following are some example errors that may occur with this
+combination::
+
+  SSL handshake failed: localhost:27017: [SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:997)
+  SSL handshake failed: localhost:27017: EOF occurred in violation of protocol (_ssl.c:997)
+
+The MongoDB server logs may show the following error::
+
+  2021-06-30T21:22:44.917+0100 E NETWORK  [conn16] SSL: error:1408A0C1:SSL routines:ssl3_get_client_hello:no shared cipher
+
+To resolve this issue, use Python <=3.10, upgrade to MongoDB 4.2+, or install
+pymongo with the :ref:`OCSP` extra which relies on PyOpenSSL.