Document the new ExceptionInfo.group_contains() method

doc/en/getting-started.rst

@@ -97,6 +97,30 @@ Use the :ref:`raises <assertraises>` helper to assert that some code raises an e
         with pytest.raises(SystemExit):
             f()
 
+You can also use the context provided by :ref:`raises <assertraises>` to
+assert that an expected exception is part of a raised ``ExceptionGroup``:
+
+.. code-block:: python
+
+    # content of test_exceptiongroup.py
+    import pytest
+
+
+    def f():
+        raise ExceptionGroup(
+            "Group message",
+            [
+                RuntimeError(),
+            ],
+        )
+
+
+    def test_exception_in_group():
+        with pytest.raises(ExceptionGroup) as excinfo:
+            f()
+        assert excinfo.group_contains(RuntimeError)
+        assert not excinfo.group_contains(TypeError)
+
 Execute the test function with “quiet” reporting mode:
 
 .. code-block:: pytest