update: entry in README & folder rename

Author: ashokdey

Diff for: README.md

@@ -39,6 +39,7 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
 - [Trees](src/_DataStructures_/Trees)
   - [Binary Search Tree](src/_DataStructures_/Trees/BST)
     - [Find k<sup>th</sup> maximum in a BST](src/_DataStructures_/Trees/BST/find-kth-max)
+    - [Find k<sup>th</sup> minimum in a BST](src/_DataStructures_/Trees/BST/find-kth-min)
   - [Suffix Tree](src/_DataStructures_/SuffixTree)
 
 ### Logical Problems