related documentation for sklearn_mixin function

Author: Leona-LYT

doc/source/example.rst

@@ -14,7 +14,8 @@ Example Gallery
    examples/FairSVM.ipynb
    examples/RankRegression.ipynb
    examples/Path_solution.ipynb
-   examples/Warm_start.ipynb   
+   examples/Warm_start.ipynb
+   examples/Sklearn_Mixin.ipynb   
 
 List of Examples
 ----------------
@@ -28,4 +29,5 @@ List of Examples
    examples/FairSVM.ipynb
    examples/RankRegression.ipynb
    examples/Path_solution.ipynb
-   examples/Warm_start.ipynb
+   examples/Warm_start.ipynb
+   examples/Sklearn_Mixin.ipynb