Add Implementation of Day 11 question (Longest Common Substring) in various languages

[MadhavBahl]

Check list:

• Created a folder with the name of language you code inside /day11/ directory (https://github.com/CodeToExpress/dailycodebase/tree/master/day11)
• Added your Codes
• Tested your codes
• Added credits (author and date) at the top of the code
• Updated README.md - https://github.com/CodeToExpress/dailycodebase/blob/master/day11/README.md
• Added yourself as a contributor using all-conributors-cli