Update contribution guidelines with ux review feedback (#6310)

Author: selenehinkley

polaris.shopify.com/content/contributing/index.md

@@ -1,6 +1,6 @@
 ---
 title: Contributing to Polaris
-description: Polaris thrives on contribution and community support. Anyone, regardless of discipline, is encouraged to contribute. No contribution is too small. We welcome everything from bug fixes or new components, to new UX guidelines. So if you find something to contribute, we hope you feel empowered to go for it. The Polaris team is here to help you along the way.
+description: Polaris exists to make a product worked on by many, feel like it was created by one person. The design system needs to stay in sync with new solutions so merchants always have a seamless experience. This is why Polaris thrives on contribution and community support. Anyone, regardless of discipline, is encouraged to contribute. No contribution is too small. We welcome everything from bug fixes or new components, to new UX guidelines. So if you find something to contribute, we hope you feel empowered to go for it. The Polaris team is here to help you along the way.
 keywords:
   - how to contribute to polaris
   - contribution