Create write-a-closures

[Magesh-sam]

Added use case for how to write a closures in javascript

Put an x inside those square brackets to mark them as complete.

• [x] Check CONTRIBUTING.md?
• [x] 1 use case per Pull Request
• [x] Double check the use case file name?
• [x] Update or remove the mdn link?
• [x] Update or remove the related use cases?
• [x] Update the category? (if necessary)
• [x] Update the date?