Update README for sorting feature

Author: ianding1

README.md

@@ -4,6 +4,8 @@
 
 Solve LeetCode problems in Vim!
 
+**Supported sorting by columns (Hooray🎉) Now you can solve problems by frequency!**
+
 This Vim plugin is inspired by [skygragon/leetcode-cli][leetcode-cli].
 
 ## Installation
@@ -70,6 +72,7 @@ Default value is `''`.
 
 ## Updates
 
+- 2019/07/28: Support showing frequencies and sorting by columns
 - 2019/07/27:
   + Support LeetCode China accounts
   + Support refreshing