Add documentation to trigger XSS

Author: jeongsoolee09

javascript/frameworks/ui5-webcomponents/test/queries/xss-input-dangerouslySetInnerHTML/README.md

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+# Minimal Demo Example of XSS in UI5-Webcomponents for React
+
+This is a minimal example to demonstrate how XSS might happen in an application written with [UI5-Webcomponents for React](https://ui5.github.io/webcomponents-react/).
+
+## Steps to trigger XSS
+
+1. `npm install` and `npm start`, navigate to `localhost:3000`
+2. Input `<img src="nonexistent.jpg" onerror="alert('xss')"/>` in the [`Input` component](https://ui5.github.io/webcomponents/components/Input/)
+