Add a link to minimalistic data structure sketches. (trekhleb#933)

Author: trekhleb

README.md

@@ -301,7 +301,8 @@ npm test -- 'playground'
 
 ### References
 
-[▶ Data Structures and Algorithms on YouTube](https://www.youtube.com/playlist?list=PLLXdhg_r2hKA7DPDsunoDZ-Z769jWn4R8)
+- [▶ Data Structures and Algorithms on YouTube](https://www.youtube.com/playlist?list=PLLXdhg_r2hKA7DPDsunoDZ-Z769jWn4R8)
+- [✍🏻 Data Structure Sketches](https://okso.app/showcase/data-structures)
 
 ### Big O Notation