updated docs

Author: kunwuz

docs/source/search_methods_index/Constrained-based causal discovery methods/PC.rst

@@ -55,7 +55,7 @@ and n_features is the number of features.
 **correction_name**. Missing value correction if using missing-value PC. Default: 'MV_Crtn_Fisher_Z'
 
 **background_knowledge**: class BackgroundKnowledge. Add prior edges according to assigned causal connections.
-For detailed usage, please kindly refer to its `usage example <https://github.com/cmu-phil/causal-learn/blob/develop/tests/TestBackgroundKnowledge.py>`_.
+For detailed usage, please kindly refer to its `usage example <https://github.com/cmu-phil/causal-learn/blob/main/tests/TestBackgroundKnowledge.py>`_.
 
 Returns
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