Update CONTRIBUTING.md

[vatsalya-vyas]

Typo Fix: "succinct" -> "a succinct"

[cla-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign the CLA at https://www.nativescript.org/cla.
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[NathanWalker]

Hey! Thanks so much for opening a pull request!

The change you've proposed is not going to be accepted because this change doesn't meaningfully improve docs, fix a bug, or otherwise improve functionality.

We absolutely want to have you as a contributor, so please take a look at our open issues for ideas, and please reach out to us on Twitter at @NativeScript with questions.

Thanks again, and we look forward to seeing more PRs from you in the future! ❤️