docs: fix link to reference (#1263)

* docs: fix link to reference

* Apply suggestions from code review

Co-authored-by: Li Jiang <bnujli@gmail.com>

---------

Co-authored-by: Li Jiang <bnujli@gmail.com>

flaml/default/greedy.py

@@ -12,7 +12,7 @@ def _augment(row):
 def construct_portfolio(regret_matrix, meta_features, regret_bound):
     """The portfolio construction algorithm.
 
-    (Reference)[https://arxiv.org/abs/2202.09927].
+    Reference: [Mining Robust Default Configurations for Resource-constrained AutoML](https://arxiv.org/abs/2202.09927).
 
     Args:
         regret_matrix: A dataframe of regret matrix.