Added description and resources to Closures - JavaScript Roadmap (#1670)

* Added resources to closures

* Added more info and made some grammatic changes.

content/roadmaps/106-javascript/content/109-javascript-functions/105-scope-and-function-stack/102-closures.md

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-# Closures
+# Closures
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+Function closures are one of the most powerful, yet most misunderstood, concepts of JavaScript that are actually really simple to understand. A closure refers to a function along with its lexical scope. It is essentially what allows us to return a function A, from another function B, that remembers the local variables defined in B, even after B exits. The idea of closures is employed in nearly every other JavaScript program, hence it's paramount for any JavaScript developer to know of it really well.
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+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.codeguage.com/courses/js/functions-closures'>JavaScript Closures - The Simplest Explanation</BadgeLink>