* add solution to a challenge
add solution to the challenge: add-a-description-to-your-package-json
* add comment to all backend challenges
The comment expllains that these challenges don't need a solution.
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- [x] I have read [freeCodeCamp's contribution guidelines](https://github.com/freeCodeCamp/freeCodeCamp/blob/master/CONTRIBUTING.md).
- [x] My pull request has a descriptive title (not a vague title like `Update index.md`)
- [x] My pull request targets the `master` branch of freeCodeCamp.
- [x] None of my changes are plagiarized from another source without proper attribution.
- [x] My article does not contain shortened URLs or affiliate links.
If your pull request closes a GitHub issue, replace the XXXXX below with the issue number.
Closes #XXXXX
