Update README.md

Author: dennisbakhuis

B_Pandas_tips/README.md

@@ -16,4 +16,5 @@ Various notebooks demostrating nifty Pandas tricks
 [9. Loc or query?](https://github.com/dennisbakhuis/Tutorials/blob/master/B_Pandas_tips/9%20-%20Query%20or%20loc.ipynb)\
 [10. Filter your rows and columns](https://github.com/dennisbakhuis/Tutorials/blob/master/B_Pandas_tips/10%20-%20Filter%20your%20rows%20and%20columns.ipynb)\
 [11. count_values like a pro](https://github.com/dennisbakhuis/Tutorials/blob/master/B_Pandas_tips/11%20-%20value_counts%20like%20a%20pro.ipynb)\
-[12. .rank() the stars in Pandas](https://github.com/dennisbakhuis/Tutorials/blob/master/B_Pandas_tips/12%20-%20Ranking%20the%20stars%20in%20Pandas.ipynb)
+[12. .rank() the stars in Pandas](https://github.com/dennisbakhuis/Tutorials/blob/master/B_Pandas_tips/12%20-%20Ranking%20the%20stars%20in%20Pandas.ipynb)\
+[13. Pivot your tables](https://github.com/dennisbakhuis/Tutorials/blob/master/B_Pandas_tips/13%20-%20Pivot%20your%20tables.ipynb)