Add README.md and demo video for Sliding TextBox component

Author: jsakamoto

.assets/demo-video.gif

@@ -0,0 +1,44 @@
+# Sliding TextBox Demo
+
+A demonstration of smooth scrolling implementation to improve readability in translation subtitle systems.
+
+When new text is added, typical implementations cause existing text to jump abruptly, making it difficult to read. The SlidingTextBox component solves this problem with smooth animation display.
+
+**Left (Normal)**: Abrupt scrolling  
+**Right (Sliding)**: Smooth slide-in animation
+
+[Demo](https://sample-by-jsakamoto.github.io/React-SlidingTextBox/)
+
+![](.assets/demo-video.gif)
+
+
+## Getting Started
+
+### Prerequisites
+
+- Node.js (v20 or later)
+- npm (Node Package Manager)
+
+### Installation
+1. Clone the repository:
+   ```bash
+   git clone https://github.com/sample-by-jsakamoto/React-SlidingTextBox.git
+   ```
+2. Navigate to the project directory:
+   ```bash
+   cd React-SlidingTextBox
+   ```
+3. Install dependencies:
+   ```bash
+   npm ci
+   ```
+### Running the Application
+
+4. Start the development server:
+   ```bash
+    npm run dev
+    ```
+
+## License
+
+This project is released into the public domain under [The Unlicense](LICENSE).