Fix ShellSort README errors (issue trekhleb#195).

Author: trekhleb

src/algorithms/sorting/shell-sort/README.md

@@ -37,6 +37,8 @@ After this step, the array should look like this
 
 ![Shellsort](https://www.tutorialspoint.com/data_structures_algorithms/images/shell_sort_step_2.jpg)
 
+> UPD: On the picture below there is a typo and result array is supposed to be `[14, 10, 27, 19, 35, 33, 42, 44]`.
+
 Finally, we sort the rest of the array using interval of value 1. 
 Shell sort uses insertion sort to sort the array.
 
@@ -50,5 +52,6 @@ Shell sort uses insertion sort to sort the array.
 
 ## References
 
-* [Tutorials Point](https://www.tutorialspoint.com/data_structures_algorithms/shell_sort_algorithm.htm)
-* [Wikipedia](https://en.wikipedia.org/wiki/Shellsort)
+- [Tutorials Point](https://www.tutorialspoint.com/data_structures_algorithms/shell_sort_algorithm.htm)
+- [Wikipedia](https://en.wikipedia.org/wiki/Shellsort)
+- [YouTube by Rob Edwards](https://www.youtube.com/watch?v=ddeLSDsYVp8&index=79&list=PLLXdhg_r2hKA7DPDsunoDZ-Z769jWn4R8)