Merge pull request #89 from amitkrxyz/amitkrxyz

Add hackerrank and onlinegdb

Author: erikw

README.md

@@ -512,7 +512,9 @@ We know that Vi-[clones](http://www.linfo.org/vi/clones.html)/derivatives have V
   * :heavy_plus_sign: ~[atom-vim-mode-plus](https://github.com/t9md/atom-vim-mode-plus)~
 
 ## Web Apps
+* :white_check_mark: [HackerRank](https://www.hackerrank.com/) - Coding challenges and interview preparation across multiple domains.
 * :white_check_mark: [leetcode](https://leetcode.com/) - Algorithmic programming problem repository.
+* :white_check_mark: [OnlineGDB](https://www.onlinegdb.com/) - Online compiler and debugger supporting many programming languages.
 * :white_check_mark: [Rust Playground](https://play.rust-lang.org/) - The editor in the rust playground has a Vim mode.
 
 ## Web browsers