Fix PR08, RT02, RT03, and SA01 on pandas.Index.fillna
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index aa22527d8c2d7..d2887c6652635 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -2126,13 +2126,18 @@ def fillna(self, value=None, downcast=None):
             Scalar value to use to fill holes (e.g. 0).
             This value cannot be a list-likes.
         downcast : dict, default is None
-            a dict of item->dtype of what to downcast if possible,
+            A dict of item->dtype of what to downcast if possible,
             or the string 'infer' which will try to downcast to an appropriate
             equal type (e.g. float64 to int64 if possible).
 
         Returns
         -------
-        filled : Index
+        Index
+
+        See Also
+        --------
+        DataFrame.fillna : Fill NaN values of a DataFrame.
+        Series.fillna : Fill NaN Values of a Series.
         """
         self._assert_can_do_op(value)
         if self.hasnans:

- [x] closes #https://github.com/pandanistas/pandanistas_sprint_ui2020/issues/5
- [ ] tests added / passed
- [x] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
