Small contribution docs update

[antonpirker]

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Thank you for contributing to sentry-python! Please add tests to validate your changes, and lint your code using tox -e linters.

Running the test suite on your PR might require maintainer approval. The AWS Lambda tests additionally require a maintainer to add a special label, and they will fail until this label is added.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
13808	1	13807	4167

View the top 1 failed tests by shortest run time

tests.test_basics test_classmethod_tracing

Stack Traces | 0.152s run time

tests/test_basics.py:946: in test_classmethod_tracing
    assert fake_start_child.call_count == 1
E   AssertionError: assert 2 == 1
E    +  where 2 = <MagicMock name='mock.start_child' id='139657650674752'>.call_count

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