Add support to record custom properties on xml output

doc/en/usage.rst

@@ -153,6 +153,15 @@ integration servers, use this invocation::
 
 to create an XML file at ``path``.
 
+If you want to log additional information for a test, you can use
+record_property("key", value)::
+
+    import pytest
+    def test_function():
+        ...
+        pytest.record_property("example_key", 1)
+        ...
+
 Creating resultlog format files
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