Added missing hyperlink and created new page for explanation of 'Closures'

[itsbittoosharma]

Description

Added missing explanation of point 'Closures' on https://nodejs.dev/learn/how-much-javascript-do-you-need-to-know-to-use-nodejs unlike other mentioned points. Also hyperlink is also added for the same on concerned page.

[mikeesto]

Thanks for the PR. Please have a look at the linting errors: https://github.com/nodejs/nodejs.dev/runs/5109592874?check_suite_focus=true . This may also help the failing build

[github-actions[bot]]

This pull request is stale because it has been open for 30 days with no activity.

[ovflowd]

Hey, @itsbittoosharma, just a friendly reminder that if you don't update this PR it will soon be closed. Kindly update the PR if possible 🙇

[github-actions[bot]]

This pull request was closed because it has been inactive for 14 days since being marked as stale.